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id: wiki-2026-0508-draw-call
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title: Draw Call
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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: [Drawcall, GPU Submit, Render Command]
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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, performance, rendering]
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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: C++/Rust
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framework: Vulkan/Metal/D3D12/WebGPU
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---
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# Draw Call
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## 매 한 줄
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> **"매 CPU 가 GPU 에게 매 한 batch 를 그리라고 매 instructing 하는 single command"**. 1990s OpenGL `glDrawArrays` 시대의 매 ms-cost overhead 가 매 modern explicit API (Vulkan/D3D12/Metal/WebGPU) + bindless + GPU-driven rendering 으로 매 micro-second 수준으로 떨어짐. 매 2026 — `vkCmdDrawIndexedIndirectCount` + mesh shader 가 매 norm.
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## 매 핵심
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### 매 anatomy
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- Set pipeline (shader, blend, depth state).
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- Bind resources (vertex/index buffer, uniform, texture).
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- Issue draw (`drawIndexed`, `dispatch`).
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- Submit to queue.
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### 매 cost source
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- **Driver validation**: legacy GL 의 매 main bottleneck.
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- **State change**: pipeline / RT / descriptor switch.
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- **CPU↔GPU sync**: fence wait, map/unmap.
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- **Command recording**: 매 modern API 에서 매 thread 분산 가능.
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### 매 응용
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1. Draw call 수 줄임 → frame time 직접 감소.
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2. Batching (instancing, atlas, indirect).
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3. GPU-driven culling (compute → indirect).
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## 💻 패턴
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### Vulkan minimal draw
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```cpp
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vkCmdBindPipeline(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline);
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VkBuffer vbs[] = {vertexBuf}; VkDeviceSize off[] = {0};
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vkCmdBindVertexBuffers(cmd, 0, 1, vbs, off);
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vkCmdBindIndexBuffer(cmd, indexBuf, 0, VK_INDEX_TYPE_UINT32);
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vkCmdBindDescriptorSets(cmd, ..., 0, 1, &set, 0, nullptr);
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vkCmdDrawIndexed(cmd, indexCount, instanceCount, 0, 0, 0);
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```
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### Instancing (1 call → N objects)
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```glsl
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// vertex shader
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layout(location = 0) in vec3 pos;
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layout(location = 4) in mat4 modelMatrix; // per-instance
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void main() { gl_Position = vp * modelMatrix * vec4(pos, 1); }
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```
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```cpp
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// CPU side
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vkCmdDrawIndexed(cmd, idxCount, 10000, 0, 0, 0); // 10k objects, 1 draw
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```
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### Indirect draw (GPU-driven)
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```cpp
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struct VkDrawIndexedIndirectCommand {
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uint32_t indexCount, instanceCount, firstIndex;
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int32_t vertexOffset; uint32_t firstInstance;
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};
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// Compute shader culls & writes commands + count to GPU buffer.
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// CPU just calls:
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vkCmdDrawIndexedIndirectCount(cmd, drawBuf, 0, countBuf, 0, MAX_DRAWS, sizeof(Cmd));
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```
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### Bindless (descriptor indexing)
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```glsl
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#extension GL_EXT_nonuniform_qualifier : require
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layout(set=0, binding=0) uniform sampler2D textures[];
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layout(push_constant) uniform PC { uint texIndex; };
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void main() { color = texture(textures[nonuniformEXT(texIndex)], uv); }
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```
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### Mesh shader (DX12 / Vulkan)
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```glsl
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#version 460
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#extension GL_EXT_mesh_shader : require
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layout(local_size_x = 32) in;
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layout(triangles, max_vertices = 64, max_primitives = 124) out;
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void main() {
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SetMeshOutputsEXT(vertCount, primCount);
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// amplify / cull per meshlet, no IA stage
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}
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```
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### Multi-thread command recording (Vulkan)
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```cpp
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// 1 secondary CB per thread
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parallel_for(0, N, [&](int i) {
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VkCommandBuffer sec = secondaryCBs[threadId];
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vkBeginCommandBuffer(sec, ...);
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record_draws_for_chunk(sec, chunk[i]);
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vkEndCommandBuffer(sec);
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});
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vkCmdExecuteCommands(primaryCB, N, secondaryCBs.data());
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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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| 同 mesh 수천 개 | Instancing |
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| Diverse mesh, frustum cullable | GPU-driven indirect + compute culling |
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| Many materials | Bindless texture + uber-shader |
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| Highly detailed geometry | Mesh shader + meshlet |
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| Legacy GL/GLES | Atlas + state sort + minimize binds |
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**기본값**: Modern → indirect + bindless. Legacy → batch by state.
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## 🔗 Graph
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- 부모: [[GPU Pipeline]] · [[Real-time Rendering]]
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- 변형: [[Indirect Draw]]
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- 응용: [[Frustum Culling]] · [[Geometry Merging]]
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- Adjacent: [[Vulkan]] · [[Metal]] · [[WebGPU]]
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## 🤖 LLM 활용
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**언제**: Renderer architecture, perf budget 분석, profiling 결과 해석.
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**언제 X**: Game design / art direction.
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## ❌ 안티패턴
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- **One draw per object**: legacy 패턴 — instancing/indirect 사용.
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- **Excessive state changes**: shader/pipeline 매 frame 수천 번 swap.
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- **CPU-side culling 만**: GPU 보내서 매 compute 로 culling.
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- **Map/unmap loop**: persistent mapped buffer + ring 사용.
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- **Single thread record**: secondary CB + parallel_for.
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## 🧪 검증 / 중복
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- Verified (Vulkan/D3D12 spec, Khronos best practices, GPU Zen).
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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 — draw call cost + indirect/bindless/mesh shader |
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