11-12-2020, 11:30 PM
The bright side of ray-traced global illumination
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<div class="item_body mobile_image_transform"> <strong><i><small> The following blog post, unless otherwise noted, was written by a member of Gamasutras community.<br />The thoughts and opinions expressed are those of the writer and not Gamasutra or its parent company. </small></i></strong> </p>
<hr>
<p data-css="tve-u-1758046d6be"><strong>[Recommended: read the original blog post “<a href="https://go.thegamedev.guru/rt-global-illumination">Unity ray-traced global illumination</a>” for proper interactive content]</strong></p>
<p data-css="tve-u-1758046d6be">Let’s get back to ray tracing with global illumination in Unity. Discover what global illumination is and choose the better fit for your game:</p>
<ul>
<li><strong>Baked GI</strong></li>
<li><strong>Screen-space Raster GI</strong></li>
<li><strong>Screen-Space Ray-traced GI</strong></li>
</ul>
<p><img alt data-height="439" data-id="9723" data-init-height="608" data-init-width="1080" data-width="780" height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-3.gif" title="Unity-Ray-Tracing-Global-Illumination-Thumbnail" width="600"></p>
<p><strong>TABLE OF CONTENTS</strong></p>
<p>1 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170145">Can You Guess What’s Missing in This Scene?</a></p>
<p>2 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170146">What’s Unity Global Illumination?</a></p>
<p>3 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170147">Your Options for Global Illumination in Unity</a></p>
<p> 3.1 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170148">Unity Baked Global Illumination</a></p>
<p> 3.2 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170149">Unity Screen-Space Global Illumination (SSGI)</a></p>
<p> 3.3 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170150">Ray-Traced Global Illumination in Unity</a></p>
<p>4 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170151">The Performance Cost of Ray-Traced Global Illumination in Unity</a></p>
<p>5 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170152">Next Steps</a></p>
<h2 id="t-1604169170145">Can You Guess What’s Missing in This Scene?</h2>
<p>Take a second to have a look at the screenshot below.</p>
<p>Can you guess what is this picture missing to be… visually “appealing”?</p>
<p><img alt data-height="439" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-2.png" width="600"></p>
<p>It’s looking either too bright or too dark. That’s not an easy thing to see in real life.</p>
<p>Why?</p>
<p>Because light bounces between surfaces.</p>
<p>These bounces soften the “transitions” between bright and dark areas. And you don’t see that happening in the screenshot above. </p>
<p>Now, let’s see something more realistic.</p>
<p>Have a look below. Use <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi1">the slider</a> to transition to a more “visually correct” scene:</p>
<p data-css="tve-u-1757ff0e4e2"><a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi1"><strong>Is Global Illumination Overrated? (Answer: NO)</strong></a></p>
<p><a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi1"><img height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-3.png" width="600"></a></p>
<p>What’s the difference?</p>
<p>Global illumination (GI). To be more specific, indirect illumination.</p>
<p>Let’s quickly explain how GI works.</p>
<h2 id="t-1604169170146">What’s Unity Global Illumination?</h2>
<p>Like I said, light rays bounce off surfaces and lose energy in the process (e.g. brightness, a change in color, etc.). Eventually, light will reach your eyes from different surfaces.</p>
<p>In graphics, we distinguish between:</p>
<ul>
<li><strong>Direct lighting</strong>: the sun light hits the floor and reflects into your eyes. That lets you see that specific fragment on the floor.</li>
<li><strong>Indirect lighting</strong>: the sun light hits the floor, bounces to your hand watch <strong>and then</strong> bounces towards someone’s eyes. That person becomes temporarily stunned.</li>
</ul>
<p>The difference is that GI takes more bounces into account. Not just one.</p>
<p>Direct lighting is easy and cheap to calculate. Indirect lighting, not so much.</p>
<p>So, how do you do indirect lighting* in Unity?</p>
<p>Here are your options.</p>
<p><em>* I use the words indirect lighting and global illumination interchangeably. In theory, they’re not the same. But in practice, we treat them as if they were.</em></p>
<h2 id="t-1604169170147">Your Options for Global Illumination in Unity</h2>
<p>Let’s build an ultra-simple scene to see and compare the different methods you have in Unity to do global illumination.</p>
<p>Here’s the scene we are building:</p>
<p><img alt data-css="tve-u-1757ff684c6" data-height="326" data-id="2075" data-init-height="312" data-init-width="300" data-tcb-events="__TCB_EVENT_[{"t":"click","a":"thrive_zoom","config":{"id":"2075","size":"full"}}]_TNEVE_BCT__" data-width="389" height="504" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-4.png" width="600"></p>
<p><em>Light Bounces Global Illumination Diagram</em></p>
<p>First, take a deep breath and enjoy my drawing skills.</p>
<p>Now, let’s explain it.</p>
<p>A wall is covering/occluding another wall, which in real-life would prevent light from reaching it.</p>
<p>However, there’s a small gap below.</p>
<p>This bottom gap will allow some sun rays to “escape” the big wall and reach the wall behind after these rays bounce off the floor.</p>
<p>The diagram is clear, right?</p>
<p>Here’s how our baseline (just direct lighting + shadows) looks in Unity.</p>
<p><img alt data-height="615" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-5.png" width="600"></p>
<p>Global Illumination Scenario</p>
<p>We won’t use that angle. It’s hard to see the effect of indirect lighting later on.</p>
<p>Here’s a better angle.</p>
<p><img alt data-height="615" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-6.png" width="600"></p>
<p>Global Illumination Baseline (No GI)</p>
<p>The wall behind is quite dark.</p>
<p>No global illumination means light is not bouncing. Our black shadow on that wall remains untouched with no secondary light rays coming in.</p>
<p>Not what you want in your game. Nope.</p>
<p>So let’s improve this scenario and add some GI with our first method: <strong>baked global illumination</strong>(Unity Lightmapper).</p>
<h3 id="t-1604169170148">Unity Baked Global Illumination</h3>
<p>Baking global illumination is the <strong>cheapest way</strong> to do global illumination.</p>
<p>We do all these expensive calculations offline (in the editor). That process produces textures that we later “<strong>paint on top</strong>” of our scene.</p>
<p>It takes some effort to get the results you want with this method, as there are many settings to play with. And <strong>baking takes time</strong>.</p>
<p>But once you get it right, it looks great.</p>
<p>In fact, it’s probably the best-looking method out there to do (static) global illumination.</p>
<p>The downsides?</p>
<p>Well, it only works with static geometry.</p>
<p>I mean, you can use light probes to add some indirect illumination to dynamic (moving) elements. But that also goes with many downsides.</p>
<p>Anyway, let’s see how it looks.</p>
<p>Use <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi2">the slider</a> to see the evolution from no GI to baked GI.</p>
<p><a href="https://www.gamasutra.com/blogs/RubenTorresBonet/20201110/373493/thegamedev.guru/unity-ray-tracing/global-illumination/#gi2"><img height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-7.png" width="600"></a>Just like I promised you, it looks more… <em>correct</em>*.</p>
<p><em>* You know what I mean. Not the simplified scene per se, but the indirect lighting.</em></p>
<p>However, did you ever play an <em>interactive</em> game with just <em>static </em>elements?</p>
<p>No, you say?</p>
<p>That’s why we need more options.</p>
<p>One is to use <a href="https://docs.unity3d.com/Manual/LightProbes.html" target="_blank" rel="noopener noreferrer">light probes</a> together with <a href="https://docs.unity3d.com/Manual/lighting-window.html" target="_blank" rel="noopener noreferrer">baked GI</a>. The issue with light probes is that you need many of them to have smooth indirect lighting transitions. And guess what? That’s going to break batching for good.</p>
<p>Let’s consider instead something else: <strong>Screen-space (Raster) Global Illumination</strong>.</p>
<h3 id="t-1604169170149">Unity Screen-Space Global Illumination (SSGI)</h3>
<p>The idea with SSGI is simple. It’s execution is not.</p>
<p>We analyze the rendered frame (G-buffer) and guesstimate the way light should bounce between surfaces that are within that frame.</p>
<p>Again, we don’t do that for the whole scene. Just for the current rendered image.</p>
<p>Doing this effect in screen-space makes this option affordable in terms of performance.</p>
<p>Use <a href="http://thegamedev.guru/unity-ray-tracing/global-illumination/#gi3">the slider below</a> to find out what <em>SSGI </em>paints on top of our baseline.</p>
<p data-css="tve-u-1757ff0e4e2"><strong>Screen-Space Global Illumination (SSGI)</strong></p>
<p><a href="https://www.gamasutra.com/blogs/RubenTorresBonet/20201110/373493/thegamedev.guru/unity-ray-tracing/global-illumination/#gi3"><img height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-8.png" width="600"></a></p>
<p>A small tint of red.</p>
<p>Not much else.</p>
<p>Here is in detail the indirect lighting that we are adding to our baseline:</p>
<p><img alt data-height="438" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="337" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-9.png" width="600"></p>
<p>Unity Global Illumination: Screen-Space Effect</p>
<p>That’s a very shy effect. Quite different from baked GI, isn’t it?</p>
<p>That’s one of the limitations of <em>SSGI</em>: accuracy. Two reasons for this:</p>
<ul>
<li>We have <strong>incomplete information</strong> (the G Buffer, information about our lights and that’s about it).</li>
<li>We have a <strong>low performance budget</strong>: we need to keep this effect cheap.</li>
</ul>
<p>But hey, it works with dynamic elements. And in real-time <img loading="lazy" alt height="32" role="img" src="https://s.w.org/images/core/emoji/13.0.0/svg/1f642.svg" width="32"></p>
<p>Can we do better?</p>
<p>Yes!</p>
<p>What if we used <strong>ray-tracing</strong> for global illumination?</p>
<p>After all, with ray-tracing we have <strong>access to off-screen data</strong>. And that removes a limitation of this method.</p>
<p>Let’s check out <strong>ray-traced SSGI</strong>.</p>
<h3 id="t-1604169170150">Ray-Traced Global Illumination in Unity</h3>
<p>This is getting exciting.</p>
<p>If your project is ray-tracing-ready, you just need to click a checkbox in your screen-space global illumination effect: <em>enable ray-tracing</em>.</p>
<p>The result?</p>
<p>Use <a href="http://thegamedev.guru/unity-ray-tracing/global-illumination/#gi4">the slider below</a> to discover it.</p>
<p data-css="tve-u-1757ff0e4e2"><strong>Ray-Traced Global Illumination</strong></p>
<p><a href="https://www.gamasutra.com/blogs/RubenTorresBonet/20201110/373493/thegamedev.guru/unity-ray-tracing/global-illumination/#gi4"><img height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-10.png" width="600"></a>Juicy.</p>
<p>Here’s the singled-out effect that ray-tracing GI is adding to our baseline:</p>
<p><img alt data-height="444" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="341" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-11.png" width="600"></p>
<p>Unity Global Illumination: Ray Traced Effect</p>
<p>Indeed, ray-tracing gets you good-looking indirect lighting. And it works with <strong>dynamic elements</strong>… in real-time.</p>
<p>Huge deal.</p>
<p>The question is, <strong>can you really afford ray-traced global illumination</strong> in Unity?</p>
<p>Let’s analyze the performance cost of these effects.</p>
<h2 id="t-1604169170151">The Performance Cost of Ray-Traced Global Illumination in Unity</h2>
<p>Here are some quick tests I ran with:</p>
<ul>
<li><strong>CPU</strong>: AMD Ryzen 2700X</li>
<li><strong>GPU</strong>: TITAN RTX beefy edition</li>
<li><strong>Dataset</strong>: 3000 frames taken on the editor</li>
<li><strong>Scene</strong>: HDRP template</li>
<li data-css="tve-u-1758049c76b"><strong>Versions</strong>: Unity 2020.2.0b7 + HDRP 10.0.1</li>
</ul>
<p><img alt data-height="439" data-id="9711" data-init-height="770" data-init-width="1368" data-width="780" height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-12.png" width="600"></p>
<p data-css="tve-u-1758049d5fa">Here are the average frame times at full-HD resolution:</p>
<ul>
<li>Baked GI: 27.64ms</li>
<li>Baked GI + SSGI (low quality): 28.19 ms</li>
<li>Baked GI + SSGI (medium quality): 30.36 ms</li>
<li>Baked GI + SSGI (high quality): 32.96 ms</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — low quality): 32.07 ms</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — medium quality): 32.88 ms</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — high quality): 34.81 ms</li>
<li>Baked GI + Ray-Traced SSGI (quality mode): <strong>107.91 ms</strong> (ouch)</li>
</ul>
<p>And here are some of these numbers at 4K resolution:</p>
<ul>
<li>Baked GI: 106.21ms</li>
<li>Baked GI + SSGI (medium quality): 114.56</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — medium quality): 119.77 ms</li>
<li>Baked GI + Ray-Traced SSGI (quality mode): <strong>421 ms</strong> (OUCH)</li>
</ul>
<p data-css="tve-u-17580009ed7"><em>Why did I take them all with baked GI, you might ask? Well, I removed the baked lightmaps and the entire scene broke for good. Like visually, all was pure white.</em></p>
<p>Don’t take these times as absolute figures.</p>
<p>After all, it’s a specific scene, a specific software/hardware setup and within the editor.</p>
<p>But you can compare the <strong>relative frame times </strong>and see how performance scales on this high-fidelity scene.</p>
<p>You get the idea.</p>
<p>Two interesting questions arise (and two subjective answers):</p>
<ul>
<li>Are we ready for 4K real-time ray-traced GI? Nope.</li>
<li>Ok, and are we ready for 1080p real-time ray-traced GI? Yeah, maybe.</li>
</ul>
<p>It depends on your game.</p>
<p>But if you put enough optimization effort into it, <strong>you can get real-time ray-tracing global illumination in. It’s feasible.</strong></p>
<p>Just run it on performance mode at 1080p and you’ll be fine on most <em>NVIDIA 2000+</em> cards (and maybe even on the <em>NVIDIA 1000</em> series).</p>
<p>And the importance of performance brings me to…</p>
<p><a href="https://go.thegamedev.guru/performance-checklist" target="_blank" rel="noopener noreferrer"><img alt data-css="tve-u-175800136b8" data-height="197" data-id="6536" data-init-height="605" data-init-width="747" data-link-wrap="true" data-width="243" height="197" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-13.png" width="243"></a></p>
<h2 id="t-1604169170152">Next Steps</h2>
<p>How much did you like real-time ray-traced global illumination?</p>
<p>Well, you can get RTGI in your game if you <strong>make enough performance room</strong> (and <a href="https://thegamedev.guru/unity-ray-tracing/5-signs-you-need-ray-tracing/" target="_blank" rel="noopener noreferrer">all other Unity ray-tracing effects</a> as well).</p>
<p>And <em>nothing better</em>* than my <a href="https://go.thegamedev.guru/performance-checklist" target="_blank" rel="noopener noreferrer">Unity Performance Optimization Checklist</a> for that.</p>
<p><em>* <a href="https://go.thegamedev.guru/consulting" target="_blank" rel="noopener noreferrer">Unity performance consulting</a> is better (but not many can’t afford it).</em></p>
<p>Till next time,</p>
<p>Ruben<br />(The Gamedev Guru)</p>
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<div class="item_body mobile_image_transform"> <strong><i><small> The following blog post, unless otherwise noted, was written by a member of Gamasutras community.<br />The thoughts and opinions expressed are those of the writer and not Gamasutra or its parent company. </small></i></strong> </p>
<hr>
<p data-css="tve-u-1758046d6be"><strong>[Recommended: read the original blog post “<a href="https://go.thegamedev.guru/rt-global-illumination">Unity ray-traced global illumination</a>” for proper interactive content]</strong></p>
<p data-css="tve-u-1758046d6be">Let’s get back to ray tracing with global illumination in Unity. Discover what global illumination is and choose the better fit for your game:</p>
<ul>
<li><strong>Baked GI</strong></li>
<li><strong>Screen-space Raster GI</strong></li>
<li><strong>Screen-Space Ray-traced GI</strong></li>
</ul>
<p><img alt data-height="439" data-id="9723" data-init-height="608" data-init-width="1080" data-width="780" height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-3.gif" title="Unity-Ray-Tracing-Global-Illumination-Thumbnail" width="600"></p>
<p><strong>TABLE OF CONTENTS</strong></p>
<p>1 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170145">Can You Guess What’s Missing in This Scene?</a></p>
<p>2 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170146">What’s Unity Global Illumination?</a></p>
<p>3 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170147">Your Options for Global Illumination in Unity</a></p>
<p> 3.1 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170148">Unity Baked Global Illumination</a></p>
<p> 3.2 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170149">Unity Screen-Space Global Illumination (SSGI)</a></p>
<p> 3.3 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170150">Ray-Traced Global Illumination in Unity</a></p>
<p>4 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170151">The Performance Cost of Ray-Traced Global Illumination in Unity</a></p>
<p>5 <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#t-1604169170152">Next Steps</a></p>
<h2 id="t-1604169170145">Can You Guess What’s Missing in This Scene?</h2>
<p>Take a second to have a look at the screenshot below.</p>
<p>Can you guess what is this picture missing to be… visually “appealing”?</p>
<p><img alt data-height="439" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-2.png" width="600"></p>
<p>It’s looking either too bright or too dark. That’s not an easy thing to see in real life.</p>
<p>Why?</p>
<p>Because light bounces between surfaces.</p>
<p>These bounces soften the “transitions” between bright and dark areas. And you don’t see that happening in the screenshot above. </p>
<p>Now, let’s see something more realistic.</p>
<p>Have a look below. Use <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi1">the slider</a> to transition to a more “visually correct” scene:</p>
<p data-css="tve-u-1757ff0e4e2"><a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi1"><strong>Is Global Illumination Overrated? (Answer: NO)</strong></a></p>
<p><a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi1"><img height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-3.png" width="600"></a></p>
<p>What’s the difference?</p>
<p>Global illumination (GI). To be more specific, indirect illumination.</p>
<p>Let’s quickly explain how GI works.</p>
<h2 id="t-1604169170146">What’s Unity Global Illumination?</h2>
<p>Like I said, light rays bounce off surfaces and lose energy in the process (e.g. brightness, a change in color, etc.). Eventually, light will reach your eyes from different surfaces.</p>
<p>In graphics, we distinguish between:</p>
<ul>
<li><strong>Direct lighting</strong>: the sun light hits the floor and reflects into your eyes. That lets you see that specific fragment on the floor.</li>
<li><strong>Indirect lighting</strong>: the sun light hits the floor, bounces to your hand watch <strong>and then</strong> bounces towards someone’s eyes. That person becomes temporarily stunned.</li>
</ul>
<p>The difference is that GI takes more bounces into account. Not just one.</p>
<p>Direct lighting is easy and cheap to calculate. Indirect lighting, not so much.</p>
<p>So, how do you do indirect lighting* in Unity?</p>
<p>Here are your options.</p>
<p><em>* I use the words indirect lighting and global illumination interchangeably. In theory, they’re not the same. But in practice, we treat them as if they were.</em></p>
<h2 id="t-1604169170147">Your Options for Global Illumination in Unity</h2>
<p>Let’s build an ultra-simple scene to see and compare the different methods you have in Unity to do global illumination.</p>
<p>Here’s the scene we are building:</p>
<p><img alt data-css="tve-u-1757ff684c6" data-height="326" data-id="2075" data-init-height="312" data-init-width="300" data-tcb-events="__TCB_EVENT_[{"t":"click","a":"thrive_zoom","config":{"id":"2075","size":"full"}}]_TNEVE_BCT__" data-width="389" height="504" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-4.png" width="600"></p>
<p><em>Light Bounces Global Illumination Diagram</em></p>
<p>First, take a deep breath and enjoy my drawing skills.</p>
<p>Now, let’s explain it.</p>
<p>A wall is covering/occluding another wall, which in real-life would prevent light from reaching it.</p>
<p>However, there’s a small gap below.</p>
<p>This bottom gap will allow some sun rays to “escape” the big wall and reach the wall behind after these rays bounce off the floor.</p>
<p>The diagram is clear, right?</p>
<p>Here’s how our baseline (just direct lighting + shadows) looks in Unity.</p>
<p><img alt data-height="615" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-5.png" width="600"></p>
<p>Global Illumination Scenario</p>
<p>We won’t use that angle. It’s hard to see the effect of indirect lighting later on.</p>
<p>Here’s a better angle.</p>
<p><img alt data-height="615" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-6.png" width="600"></p>
<p>Global Illumination Baseline (No GI)</p>
<p>The wall behind is quite dark.</p>
<p>No global illumination means light is not bouncing. Our black shadow on that wall remains untouched with no secondary light rays coming in.</p>
<p>Not what you want in your game. Nope.</p>
<p>So let’s improve this scenario and add some GI with our first method: <strong>baked global illumination</strong>(Unity Lightmapper).</p>
<h3 id="t-1604169170148">Unity Baked Global Illumination</h3>
<p>Baking global illumination is the <strong>cheapest way</strong> to do global illumination.</p>
<p>We do all these expensive calculations offline (in the editor). That process produces textures that we later “<strong>paint on top</strong>” of our scene.</p>
<p>It takes some effort to get the results you want with this method, as there are many settings to play with. And <strong>baking takes time</strong>.</p>
<p>But once you get it right, it looks great.</p>
<p>In fact, it’s probably the best-looking method out there to do (static) global illumination.</p>
<p>The downsides?</p>
<p>Well, it only works with static geometry.</p>
<p>I mean, you can use light probes to add some indirect illumination to dynamic (moving) elements. But that also goes with many downsides.</p>
<p>Anyway, let’s see how it looks.</p>
<p>Use <a href="https://thegamedev.guru/unity-ray-tracing/global-illumination/#gi2">the slider</a> to see the evolution from no GI to baked GI.</p>
<p><a href="https://www.gamasutra.com/blogs/RubenTorresBonet/20201110/373493/thegamedev.guru/unity-ray-tracing/global-illumination/#gi2"><img height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-7.png" width="600"></a>Just like I promised you, it looks more… <em>correct</em>*.</p>
<p><em>* You know what I mean. Not the simplified scene per se, but the indirect lighting.</em></p>
<p>However, did you ever play an <em>interactive</em> game with just <em>static </em>elements?</p>
<p>No, you say?</p>
<p>That’s why we need more options.</p>
<p>One is to use <a href="https://docs.unity3d.com/Manual/LightProbes.html" target="_blank" rel="noopener noreferrer">light probes</a> together with <a href="https://docs.unity3d.com/Manual/lighting-window.html" target="_blank" rel="noopener noreferrer">baked GI</a>. The issue with light probes is that you need many of them to have smooth indirect lighting transitions. And guess what? That’s going to break batching for good.</p>
<p>Let’s consider instead something else: <strong>Screen-space (Raster) Global Illumination</strong>.</p>
<h3 id="t-1604169170149">Unity Screen-Space Global Illumination (SSGI)</h3>
<p>The idea with SSGI is simple. It’s execution is not.</p>
<p>We analyze the rendered frame (G-buffer) and guesstimate the way light should bounce between surfaces that are within that frame.</p>
<p>Again, we don’t do that for the whole scene. Just for the current rendered image.</p>
<p>Doing this effect in screen-space makes this option affordable in terms of performance.</p>
<p>Use <a href="http://thegamedev.guru/unity-ray-tracing/global-illumination/#gi3">the slider below</a> to find out what <em>SSGI </em>paints on top of our baseline.</p>
<p data-css="tve-u-1757ff0e4e2"><strong>Screen-Space Global Illumination (SSGI)</strong></p>
<p><a href="https://www.gamasutra.com/blogs/RubenTorresBonet/20201110/373493/thegamedev.guru/unity-ray-tracing/global-illumination/#gi3"><img height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-8.png" width="600"></a></p>
<p>A small tint of red.</p>
<p>Not much else.</p>
<p>Here is in detail the indirect lighting that we are adding to our baseline:</p>
<p><img alt data-height="438" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="337" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-9.png" width="600"></p>
<p>Unity Global Illumination: Screen-Space Effect</p>
<p>That’s a very shy effect. Quite different from baked GI, isn’t it?</p>
<p>That’s one of the limitations of <em>SSGI</em>: accuracy. Two reasons for this:</p>
<ul>
<li>We have <strong>incomplete information</strong> (the G Buffer, information about our lights and that’s about it).</li>
<li>We have a <strong>low performance budget</strong>: we need to keep this effect cheap.</li>
</ul>
<p>But hey, it works with dynamic elements. And in real-time <img loading="lazy" alt height="32" role="img" src="https://s.w.org/images/core/emoji/13.0.0/svg/1f642.svg" width="32"></p>
<p>Can we do better?</p>
<p>Yes!</p>
<p>What if we used <strong>ray-tracing</strong> for global illumination?</p>
<p>After all, with ray-tracing we have <strong>access to off-screen data</strong>. And that removes a limitation of this method.</p>
<p>Let’s check out <strong>ray-traced SSGI</strong>.</p>
<h3 id="t-1604169170150">Ray-Traced Global Illumination in Unity</h3>
<p>This is getting exciting.</p>
<p>If your project is ray-tracing-ready, you just need to click a checkbox in your screen-space global illumination effect: <em>enable ray-tracing</em>.</p>
<p>The result?</p>
<p>Use <a href="http://thegamedev.guru/unity-ray-tracing/global-illumination/#gi4">the slider below</a> to discover it.</p>
<p data-css="tve-u-1757ff0e4e2"><strong>Ray-Traced Global Illumination</strong></p>
<p><a href="https://www.gamasutra.com/blogs/RubenTorresBonet/20201110/373493/thegamedev.guru/unity-ray-tracing/global-illumination/#gi4"><img height="473" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-10.png" width="600"></a>Juicy.</p>
<p>Here’s the singled-out effect that ray-tracing GI is adding to our baseline:</p>
<p><img alt data-height="444" data-id="2075" data-init-height="312" data-init-width="300" data-width="780" height="341" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-11.png" width="600"></p>
<p>Unity Global Illumination: Ray Traced Effect</p>
<p>Indeed, ray-tracing gets you good-looking indirect lighting. And it works with <strong>dynamic elements</strong>… in real-time.</p>
<p>Huge deal.</p>
<p>The question is, <strong>can you really afford ray-traced global illumination</strong> in Unity?</p>
<p>Let’s analyze the performance cost of these effects.</p>
<h2 id="t-1604169170151">The Performance Cost of Ray-Traced Global Illumination in Unity</h2>
<p>Here are some quick tests I ran with:</p>
<ul>
<li><strong>CPU</strong>: AMD Ryzen 2700X</li>
<li><strong>GPU</strong>: TITAN RTX beefy edition</li>
<li><strong>Dataset</strong>: 3000 frames taken on the editor</li>
<li><strong>Scene</strong>: HDRP template</li>
<li data-css="tve-u-1758049c76b"><strong>Versions</strong>: Unity 2020.2.0b7 + HDRP 10.0.1</li>
</ul>
<p><img alt data-height="439" data-id="9711" data-init-height="770" data-init-width="1368" data-width="780" height="338" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-12.png" width="600"></p>
<p data-css="tve-u-1758049d5fa">Here are the average frame times at full-HD resolution:</p>
<ul>
<li>Baked GI: 27.64ms</li>
<li>Baked GI + SSGI (low quality): 28.19 ms</li>
<li>Baked GI + SSGI (medium quality): 30.36 ms</li>
<li>Baked GI + SSGI (high quality): 32.96 ms</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — low quality): 32.07 ms</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — medium quality): 32.88 ms</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — high quality): 34.81 ms</li>
<li>Baked GI + Ray-Traced SSGI (quality mode): <strong>107.91 ms</strong> (ouch)</li>
</ul>
<p>And here are some of these numbers at 4K resolution:</p>
<ul>
<li>Baked GI: 106.21ms</li>
<li>Baked GI + SSGI (medium quality): 114.56</li>
<li>Baked GI + Ray-Traced SSGI (performance mode — medium quality): 119.77 ms</li>
<li>Baked GI + Ray-Traced SSGI (quality mode): <strong>421 ms</strong> (OUCH)</li>
</ul>
<p data-css="tve-u-17580009ed7"><em>Why did I take them all with baked GI, you might ask? Well, I removed the baked lightmaps and the entire scene broke for good. Like visually, all was pure white.</em></p>
<p>Don’t take these times as absolute figures.</p>
<p>After all, it’s a specific scene, a specific software/hardware setup and within the editor.</p>
<p>But you can compare the <strong>relative frame times </strong>and see how performance scales on this high-fidelity scene.</p>
<p>You get the idea.</p>
<p>Two interesting questions arise (and two subjective answers):</p>
<ul>
<li>Are we ready for 4K real-time ray-traced GI? Nope.</li>
<li>Ok, and are we ready for 1080p real-time ray-traced GI? Yeah, maybe.</li>
</ul>
<p>It depends on your game.</p>
<p>But if you put enough optimization effort into it, <strong>you can get real-time ray-tracing global illumination in. It’s feasible.</strong></p>
<p>Just run it on performance mode at 1080p and you’ll be fine on most <em>NVIDIA 2000+</em> cards (and maybe even on the <em>NVIDIA 1000</em> series).</p>
<p>And the importance of performance brings me to…</p>
<p><a href="https://go.thegamedev.guru/performance-checklist" target="_blank" rel="noopener noreferrer"><img alt data-css="tve-u-175800136b8" data-height="197" data-id="6536" data-init-height="605" data-init-width="747" data-link-wrap="true" data-width="243" height="197" loading="lazy" src="https://www.sickgaming.net/blog/wp-content/uploads/2020/11/the-bright-side-of-ray-traced-global-illumination-13.png" width="243"></a></p>
<h2 id="t-1604169170152">Next Steps</h2>
<p>How much did you like real-time ray-traced global illumination?</p>
<p>Well, you can get RTGI in your game if you <strong>make enough performance room</strong> (and <a href="https://thegamedev.guru/unity-ray-tracing/5-signs-you-need-ray-tracing/" target="_blank" rel="noopener noreferrer">all other Unity ray-tracing effects</a> as well).</p>
<p>And <em>nothing better</em>* than my <a href="https://go.thegamedev.guru/performance-checklist" target="_blank" rel="noopener noreferrer">Unity Performance Optimization Checklist</a> for that.</p>
<p><em>* <a href="https://go.thegamedev.guru/consulting" target="_blank" rel="noopener noreferrer">Unity performance consulting</a> is better (but not many can’t afford it).</em></p>
<p>Till next time,</p>
<p>Ruben<br />(The Gamedev Guru)</p>
</p></div>
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