From 398d181e3f9acb299b0b0881de9e735e48dc674e Mon Sep 17 00:00:00 2001
From: Sergii Liebodkin <s.lebedkin@gmail.com>
Date: Tue, 16 Apr 2024 11:29:11 +0300
Subject: [PATCH] wg_engine: added preallocated index buffers for triangle fans
 [issues 1479: lottie](#1479)

---
 src/renderer/wg_engine/tvgWgCommon.cpp | 27 ++++++++++++++++++++++++++
 src/renderer/wg_engine/tvgWgCommon.h   |  2 ++
 2 files changed, 29 insertions(+)

diff --git a/src/renderer/wg_engine/tvgWgCommon.cpp b/src/renderer/wg_engine/tvgWgCommon.cpp
index 2c7f9953..d26cd0a3 100644
--- a/src/renderer/wg_engine/tvgWgCommon.cpp
+++ b/src/renderer/wg_engine/tvgWgCommon.cpp
@@ -94,11 +94,14 @@ void WgContext::initialize()
     assert(samplerNearest);
     samplerLinear = createSampler(WGPUFilterMode_Linear, WGPUMipmapFilterMode_Linear);
     assert(samplerLinear);
+    allocateIndexBufferFan(1024);
+    assert(indexBufferFan);
 }
 
 
 void WgContext::release()
 {
+    releaseBuffer(indexBufferFan);
     releaseSampler(samplerNearest);
     releaseSampler(samplerLinear);
     if (device) {
@@ -281,6 +284,30 @@ void WgContext::allocateIndexBuffer(WGPUBuffer& buffer, const void *data, uint64
 }
 
 
+void WgContext::allocateIndexBufferFan(uint64_t vertsCount)
+{
+    assert(vertsCount >= 3);
+    uint64_t indexCount = (vertsCount - 2) * 3;
+    if ((!indexBufferFan) || (wgpuBufferGetSize(indexBufferFan) < indexCount * sizeof(uint32_t))) {
+        Array<uint32_t> indexes(indexCount);
+        for (size_t i = 0; i < vertsCount - 2; i++) {
+            indexes.push(0);
+            indexes.push(i + 1);
+            indexes.push(i + 2);
+        }
+        releaseBuffer(indexBufferFan);
+        WGPUBufferDescriptor bufferDesc{};
+        bufferDesc.nextInChain = nullptr;
+        bufferDesc.label = "The index buffer";
+        bufferDesc.usage = WGPUBufferUsage_CopyDst | WGPUBufferUsage_Index;
+        bufferDesc.size = indexCount * sizeof(uint32_t);
+        bufferDesc.mappedAtCreation = false;
+        indexBufferFan = wgpuDeviceCreateBuffer(device, &bufferDesc);
+        wgpuQueueWriteBuffer(queue, indexBufferFan, 0, &indexes[0], indexCount * sizeof(uint32_t));
+    }
+}
+
+
 void WgContext::releaseVertexBuffer(WGPUBuffer& buffer)
 {
     releaseBuffer(buffer);
diff --git a/src/renderer/wg_engine/tvgWgCommon.h b/src/renderer/wg_engine/tvgWgCommon.h
index 2415754a..668552a9 100644
--- a/src/renderer/wg_engine/tvgWgCommon.h
+++ b/src/renderer/wg_engine/tvgWgCommon.h
@@ -54,6 +54,7 @@ struct WgContext {
 
     WGPUSampler samplerNearest{};
     WGPUSampler samplerLinear{};
+    WGPUBuffer indexBufferFan{};
 
     WgPipelines* pipelines{}; // external handle (do not release)
     
@@ -75,6 +76,7 @@ struct WgContext {
 
     void allocateVertexBuffer(WGPUBuffer& buffer, const void *data, uint64_t size);
     void allocateIndexBuffer(WGPUBuffer& buffer, const void *data, uint64_t size);
+    void allocateIndexBufferFan(uint64_t size);
     void releaseVertexBuffer(WGPUBuffer& buffer);
     void releaseIndexBuffer(WGPUBuffer& buffer);
 };