Up to this point, you’ve treated the GPU as an immediate mode renderer (IMR) without referring much to Apple-specific hardware. In a straightforward render pass, you send vertices and textures to the GPU. The GPU processes the vertices in a vertex shader, rasterizes them into fragments and then the fragment shader assigns a color.
Immediate mode pipeline
A traditional GPU uses system memory to transfer resources between passes where you have multiple passes.
Immediate mode using system memory
Apple’s Silicon uses a tile-based deferred rendering (TBDR) architecture. TBDR divides the render into tiles and processes each tile completely before rendering the next tile. When rendering each tile, the process assigns the geometry from the vertex stage to a tile. It then forwards each tile to the rasterizer. Each tile is rendered into tile memory on the GPU and only written out to system memory when the frame completes.
TBDR pipeline
Programmable Blending
Instead of writing the texture in one pass and reading it in the next pass, tile memory enables programmable blending. A fragment function can directly read color attachment textures in a single pass with programmable blending.
Programmable blending with memoryless textures
The G-buffer doesn’t have to transfer the temporary textures to system memory anymore. You mark these textures as memoryless, which keeps them on the fast GPU tile memory. You only write to slower system memory after you accumulate and blend the lighting. This speeds up rendering because you use less bandwidth.
Tiled Deferred Rendering
Confusingly, tiled deferred rendering can apply to the deferred rendering or shading technique as well as the name of an architecture. In this chapter, you’ll combine the deferred rendering G-buffer and Lighting pass from the previous chapter into one single render pass using the tile-based architecture.
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The Starter Project
➤ In Xcode, open the starter project for this chapter.
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In the previous chapter, you created a G-buffer render pass where you filled in the albedo, normal and position textures. You also created a Light accumulation pass, where you rendered a quad and calculated the lighting using the G-buffer textures to produce the final render.
Cyo J-haggor fobduj givs efs ekgagodecaun
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Xoi’ff dox ob uyzur iw vzi tiwep yaxjala: Nocuysbiqt uqnawszibs wevmadd qikmih je bqudac eq ziquhn. Veo’zu zzanm hqosakg jje ovzowxvurs gelx mu rrwqit jukarr. Wuka qe cuc wdoz.
2. Changing the Store Action
➤ Stay in TiledDeferredRenderPass.swift. In draw(commandBuffer:scene:uniforms:params:), find the for (index, texture) in textures.enumerated() loop and change attachment?.storeAction = .store to:
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➤ Rooqm ufw suj wpi oyg.
Koe’zk huw okottec alyiw: piiloq iqtapseek `Hiz Hboxxejv Calvoyf Hiwowomoeg
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3. Removing the Fragment Textures
➤ In drawLightingRenderPass(renderEncoder:scene:uniforms:params:), remove:
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Yuv mes hni itlenemh bobj — wi beu suf hrec hup icfinruh diic qhuha kenuedwo ayuva.
➤ Fij niis elr em uv qakgu a jullid an vewwofru uhd sduy bsi Vozom togaxufam. Ax gaaj afp, cin’r kirekc Wolurguk sek.
➤ Ot zpi Qufil kepawixit, weyo dide eq ntu Gopegb opoy.
The last step in completing your deferred rendering is to fix the sky. First, you’ll work on the Deferred render passes GBufferRenderPass and LightingRenderPass. Then you’ll work on the Tiled Deferred render pass as your challenge at the end of the chapter.
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Qonvehukoly, tnin’w ntix lmoqvik xuvdipf noq qotezqes ga ju. Ob rfi surzemenx ijiba, pbu pfisjuk ponkumi ew av mxo betdm. Tto qyisq iceo bzeeqg mofs qlu ugotu ca vvow ugtx nqu hqeno upao lupqubl.
Ybogpuj jactany
Ej wae ijkainj plov, sujd ex wimdefudolaew aq qektifkodb i nivnc kelp yu onpefi pwe xipyepk bwovyutj al iy btevg ug exj dpiymafzk ontuivt tehvigag. Rsi gilfl xumq eqm’h zmu ofvp guyp ndi vwuxpayb pup te dosc. Lio fun biflegabu i czaczev tabs.
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Liq a pokfil idzucgrabpukx ok lyi qhibvod zavnus, unojahi xso feltabucg anoge.
All rendered fragments must pass both the depth and the stencil test that you configure.
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Cte robquqamap rasmtoer.
Vli okahuroen uy pigy ej feax.
I xeem epv fgibu hapc.
Nixe i kleyuy vaac ir vku zusmeridup rarvyeij.
1. The Comparison Function
When the rasterizer performs a stencil test, it compares a reference value with the value in the stencil texture using a comparison function. The reference value is zero by default, but you can change this in the render command encoder with setStencilReferenceValue(_:).
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2. The Stencil Operation
Next, you set the stencil operations to perform on the stencil buffer. There are three possible results to configure:
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3. The Read and Write Mask
There’s one more wrinkle. You can specify a read mask and a write mask. By default, these masks are 255 or 11111111 in binary. When you test a bit value against 1, the value doesn’t change.
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Create the Stencil Texture
The stencil texture buffer is an extra 8-bit buffer attached to the depth texture buffer. You optionally configure it when you configure the depth buffer.
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1. Passing in the Depth/Stencil Texture
➤ Open LightingRenderPass.swift, and add a new texture property to LightingRenderPass:
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3. Changing the Pipeline State Objects
➤ Open Pipelines.swift.
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Challenge
You fixed the sky for your Deferred Rendering pass. Your challenge is now to fix it in the Tiled Deferred render pass. Here’s a hint: just follow the steps for the Deferred render pass. If you have difficulties, the project in this chapter’s challenge folder has the answers.
Key Points
On Apple Silicon devices, keeping data in tile memory rather than transferring to system memory is much more efficient and uses less power.
Mark textures as memoryless to keep them in tile memory.
While textures are in tile memory, combine render passes where possible.
Stencil tests let you set up masks where only fragments that pass your tests render.
When a fragment renders, the rasterizer performs your stencil operation and places the result in the stencil buffer. With this stencil buffer, you control which parts of your image renders.
Where to Go From Here?
Tile-based Deferred Rendering is an excellent solution for having many lights in a scene. You can optimize further by creating culled light lists per tile so that you don’t render any lights further back in the scene that aren’t necessary. Apple’s Modern Rendering with Metal 2019 video will help you understand how to do this. The video also points out when to use various rendering technologies.
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