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id: wiki-2026-0508-indirect-draw
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title: Indirect Draw
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category: 10_Wiki/Topics
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status: verified
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canonical_id: self
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aliases: [Indirect Drawing, GPU-Driven Rendering, drawIndirect]
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duplicate_of: none
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source_trust_level: A
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confidence_score: 0.9
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verification_status: applied
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tags: [graphics, gpu, webgpu, vulkan, rendering, performance]
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raw_sources: []
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last_reinforced: 2026-05-10
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github_commit: pending
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tech_stack:
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language: wgsl
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framework: webgpu
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---
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# Indirect Draw
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## 매 한 줄
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> **"매 indirect draw 는 draw call args 의 GPU buffer 의 read — CPU roundtrip 없이 GPU 의 self-dispatch"**. 2026 의 GPU-driven rendering pipeline 의 foundation: Vulkan/D3D12/Metal/WebGPU 의 support. 매 culling, LOD, instancing 의 GPU 에서 결정 → CPU draw-call overhead 의 elimination.
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## 매 핵심
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### 매 vs Direct Draw
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- **Direct**: `draw(vertexCount, instanceCount, firstVertex, firstInstance)` — args from CPU.
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- **Indirect**: `drawIndirect(buffer, offset)` — args read from GPU buffer.
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- **Multi-draw indirect (MDI)**: thousands of draws from one CPU command.
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### 매 Args Layout (WebGPU)
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```
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struct DrawIndirectArgs {
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vertexCount: u32,
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instanceCount: u32,
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firstVertex: u32,
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firstInstance: u32,
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}
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struct DrawIndexedIndirectArgs {
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indexCount: u32,
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instanceCount: u32,
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firstIndex: u32,
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baseVertex: i32,
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firstInstance: u32,
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}
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```
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### 매 Pipeline (GPU-driven)
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1. Compute shader: per-object frustum/occlusion cull → write visible list.
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2. Compute shader: write indirect args buffer (instanceCount=0 for culled).
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3. `drawIndexedIndirect` (or MDI) reads buffer → renders only visible.
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### 매 응용
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1. Massive instanced scenes (foliage, crowds, particles).
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2. GPU-driven culling (frustum, occlusion via Hi-Z).
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3. LOD selection on GPU.
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4. Variable-rate / batched rendering (cluster culling, Nanite-style).
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## 💻 패턴
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### WebGPU Indirect Draw Setup
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```ts
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// Args buffer (visible after compute)
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const indirectBuffer = device.createBuffer({
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size: 16, // 4 u32
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usage: GPUBufferUsage.INDIRECT | GPUBufferUsage.STORAGE | GPUBufferUsage.COPY_DST,
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});
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// Initialize: 36 verts, 1000 instances, offset 0/0
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device.queue.writeBuffer(indirectBuffer, 0,
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new Uint32Array([36, 1000, 0, 0]));
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// In render pass
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pass.setPipeline(pipeline);
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pass.setVertexBuffer(0, vertices);
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pass.drawIndirect(indirectBuffer, 0);
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```
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### Culling Compute Shader (WGSL)
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```wgsl
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struct DrawArgs { vertexCount: u32, instanceCount: u32,
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firstVertex: u32, firstInstance: u32 }
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@group(0) @binding(0) var<storage, read> objects: array<Object>;
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@group(0) @binding(1) var<storage, read_write> drawArgs: DrawArgs;
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@group(0) @binding(2) var<storage, read_write> visibleInstances: array<u32>;
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@group(0) @binding(3) var<uniform> camera: Camera;
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@compute @workgroup_size(64)
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fn cullCS(@builtin(global_invocation_id) gid: vec3<u32>) {
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let i = gid.x;
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if (i >= arrayLength(&objects)) { return; }
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let obj = objects[i];
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if (frustumTest(obj.bounds, camera.frustum)) {
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let slot = atomicAdd(&drawArgs.instanceCount, 1u);
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visibleInstances[slot] = i;
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}
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}
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```
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### Reset Pass (clear instanceCount)
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```ts
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// Each frame, before culling, zero out instanceCount
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device.queue.writeBuffer(indirectBuffer, 4, new Uint32Array([0]));
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```
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### Multi-Draw Indirect (Vulkan)
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```cpp
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// Draw N different meshes from one buffer
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vkCmdDrawIndexedIndirect(cmd, indirectBuf, 0,
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/*drawCount*/ N,
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/*stride*/ sizeof(VkDrawIndexedIndirectCommand));
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// Or with count buffer (drawCount is itself on GPU)
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vkCmdDrawIndexedIndirectCount(cmd, indirectBuf, 0,
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countBuf, 0, /*maxDraws*/ N,
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sizeof(VkDrawIndexedIndirectCommand));
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```
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### Three.js (R175+ has WebGPU)
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```js
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import { WebGPURenderer, BatchedMesh } from 'three';
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const renderer = new WebGPURenderer();
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// BatchedMesh internally uses indirect draw + instancing
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const batched = new BatchedMesh(maxInstances, maxVerts, maxIndices);
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batched.addGeometry(geom1);
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batched.addGeometry(geom2);
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// One draw call, GPU handles per-instance state
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```
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### Hi-Z Occlusion Culling (sketch)
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```wgsl
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// Sample Hi-Z mip — fastest mip where bounding sphere covers >1 texel
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fn occluded(bsphere: vec4<f32>) -> bool {
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let screenRect = projectToScreen(bsphere);
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let mip = computeMip(screenRect);
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let depth = textureSampleLevel(hiZ, samp, screenRect.center, mip).r;
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return bsphereMinDepth(bsphere) > depth;
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}
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```
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## 매 결정 기준
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| 상황 | Approach |
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|---|---|
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| <100 unique objects | Direct draw / instancing — overhead 의 not worth |
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| 1k-1M instances | Indirect draw + GPU cull |
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| Many distinct meshes | Multi-draw indirect (Vulkan/D3D12); WebGPU 의 batched |
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| Foliage/crowd | Indirect + GPU LOD selection |
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| Mobile / low-end | Direct draw (compute overhead 의 watch) |
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**기본값**: large dynamic scene 의 GPU-driven indirect pipeline. Small scene 의 direct draw.
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## 🔗 Graph
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- 부모: [[Graphics Pipeline]]
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- 변형: [[GPU-Driven Rendering]]
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- 응용: [[Frustum Culling]] · [[Nanite]]
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- Adjacent: [[WebGPU]] · [[Vulkan]] · [[Compute Shader]]
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## 🤖 LLM 활용
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**언제**: GPU-driven pipeline 의 design, culling 의 implement, draw-call overhead 의 reduce.
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**언제 X**: simple scene 의 indirect draw 의 over-engineering — direct 의 fine.
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## ❌ 안티패턴
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- **CPU readback of indirect buffer**: 매 stall. GPU 의 self-contained 의 keep.
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- **Per-frame full buffer rewrite**: defeats purpose. 매 GPU compute 의 update.
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- **No Hi-Z for occlusion**: false positives — Hi-Z 또는 conservative AABB 의 사용.
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- **Indirect for tiny scenes**: compute dispatch overhead > savings.
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- **WebGL fallback assumed**: WebGL 의 no indirect draw — WebGPU required.
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## 🧪 검증 / 중복
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- Verified (WebGPU spec, Vulkan spec, GPU Gems / Activision Nanite paper).
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- 신뢰도 A.
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## 🕓 Changelog
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| 날짜 | 변경 |
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| 2026-05-08 | Phase 1 |
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| 2026-05-10 | Manual cleanup — indirect draw / GPU-driven rendering full content |
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