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[glTF] Load UINT8 indices into UINT16 buffer
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While glTF supports specifying indices in UINT8, Vulkan only supports
UINT16 and UINT32 index buffers (without extensions). If we detect a
UINT8 index buffer (componentType = 5121) then we repack it into the
next best thing: a UINT16 buffer. This increases the size of the indices
in the resulting repacked GPU buffer but allows us to support these
scenes without extensions.

This allows us to load more Khronos glTF-Sample-Assets like
TextureCoordinateTest.

Fixes google#453
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@footballhead
footballhead committed Jun 11, 2024
1 parent 78e19af commit 141a363
Showing 1 changed file with 39 additions and 19 deletions.
58 changes: 39 additions & 19 deletions src/ppx/scene/scene_gltf_loader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1243,22 +1243,28 @@ ppx::Result GltfLoader::LoadMeshData(

struct BatchInfo
{
scene::MaterialRef material = nullptr;
uint32_t indexDataOffset = 0; // Must have 4 byte alignment
uint32_t indexDataSize = 0;
uint32_t positionDataOffset = 0; // Must have 4 byte alignment
uint32_t positionDataSize = 0;
uint32_t attributeDataOffset = 0; // Must have 4 byte alignment
uint32_t attributeDataSize = 0;
grfx::Format indexFormat = grfx::FORMAT_UNDEFINED;
uint32_t indexCount = 0;
uint32_t vertexCount = 0;
ppx::AABB boundingBox = {};
scene::MaterialRef material = nullptr;
// Start of the index plane in the final repacked GPU buffer.
uint32_t indexDataOffset = 0; // Must have 4 byte alignment
// Total size of the index plane in the final repacked GPU buffer.
uint32_t indexDataSize = 0;
uint32_t positionDataOffset = 0; // Must have 4 byte alignment
uint32_t positionDataSize = 0;
uint32_t attributeDataOffset = 0; // Must have 4 byte alignment
uint32_t attributeDataSize = 0;
// Format of the input index buffer.
grfx::Format indexFormat = grfx::FORMAT_UNDEFINED;
// Format of the index plane in the final repacked GPU buffer.
grfx::Format repackedIndexFormat = grfx::FORMAT_UNDEFINED;
// How many indices are in the input index buffer.
uint32_t indexCount = 0;
uint32_t vertexCount = 0;
ppx::AABB boundingBox = {};
};

// Build out batch infos
std::vector<BatchInfo> batchInfos;
//
// Size of the final GPU buffer to allocate. Must account for growth during repacking.
uint32_t totalDataSize = 0;
//
for (cgltf_size primIdx = 0; primIdx < pGltfMesh->primitives_count; ++primIdx) {
Expand All @@ -1279,18 +1285,23 @@ ppx::Result GltfLoader::LoadMeshData(
// Get index format
//
// It's valid for this to be UNDEFINED, means the primitive doesn't have any index data.
// However, if it's not UNDEFINED, UINT16, or UINT32 then it's a format we can't handle.
// However, if it's not UNDEFINED, UINT8, UINT16, or UINT32 then it's a format we can't handle.
//
auto indexFormat = GetFormat(pGltfPrimitive->indices);
if ((indexFormat != grfx::FORMAT_UNDEFINED) && (indexFormat != grfx::FORMAT_R16_UINT) && (indexFormat != grfx::FORMAT_R32_UINT)) {
PPX_ASSERT_MSG(false, "GLTF mesh primitive has unrecognized index format");
if ((indexFormat != grfx::FORMAT_UNDEFINED) && (indexFormat != grfx::FORMAT_R8_UINT) && (indexFormat != grfx::FORMAT_R16_UINT) && (indexFormat != grfx::FORMAT_R32_UINT)) {
PPX_ASSERT_MSG(false, "GLTF mesh primitive has unrecognized index format: " << ToString(indexFormat));
return ppx::ERROR_SCENE_INVALID_SOURCE_GEOMETRY_INDEX_TYPE;
}

// Index data size
// Vulkan doesn't support 8 bit index buffers without extensions so use the next smallest format instead
auto repackedIndexFormat = indexFormat == grfx::FORMAT_R8_UINT ? grfx::FORMAT_R16_UINT : indexFormat;

// Index data size of input
const uint32_t indexCount = !IsNull(pGltfPrimitive->indices) ? static_cast<uint32_t>(pGltfPrimitive->indices->count) : 0;
const uint32_t indexElementSize = grfx::GetFormatDescription(indexFormat)->bytesPerTexel;
const uint32_t indexDataSize = indexCount * indexElementSize;
// If we repack indices into a larger buffer then we need to account for growth
const uint32_t repackedSizeRatio = grfx::GetFormatDescription(repackedIndexFormat)->bytesPerTexel / indexElementSize;
const uint32_t indexDataSize = indexCount * indexElementSize * repackedSizeRatio;

// Get position accessor
const VertexAccessors gltflAccessors = GetVertexAccessors(pGltfPrimitive);
Expand All @@ -1304,7 +1315,7 @@ ppx::Result GltfLoader::LoadMeshData(
const uint32_t positionDataSize = vertexCount * targetPositionElementSize;
const uint32_t attributeDataSize = vertexCount * targetAttributesElementSize;

// Index data offset
// Index data offset into final GPU buffer; account for potential growth from repacking indices into a larger buffer
const uint32_t indexDataOffset = totalDataSize;
totalDataSize += RoundUp<uint32_t>(indexDataSize, 4);
// Position data offset
Expand All @@ -1323,6 +1334,7 @@ ppx::Result GltfLoader::LoadMeshData(
batchInfo.attributeDataOffset = attributeDataOffset;
batchInfo.attributeDataSize = attributeDataSize;
batchInfo.indexFormat = indexFormat;
batchInfo.repackedIndexFormat = repackedIndexFormat;
batchInfo.indexCount = indexCount;

// Material
Expand Down Expand Up @@ -1415,6 +1427,7 @@ ppx::Result GltfLoader::LoadMeshData(
if (batch.indexFormat == grfx::FORMAT_UNDEFINED) {
genTopologyIndices = true;
batch.indexFormat = (batch.vertexCount < 65536) ? grfx::FORMAT_R16_UINT : grfx::FORMAT_R32_UINT;
batch.repackedIndexFormat = batch.indexFormat;
}

// Create genTopologyIndices so we can repack gemetry data into position planar + packed vertex attributes.
Expand All @@ -1423,7 +1436,7 @@ ppx::Result GltfLoader::LoadMeshData(
//
{
auto createInfo = hasAttributes ? GeometryCreateInfo::PositionPlanarU16() : GeometryCreateInfo::PlanarU16();
if (batch.indexFormat == grfx::FORMAT_R32_UINT) {
if (batch.repackedIndexFormat == grfx::FORMAT_R32_UINT) {
createInfo = hasAttributes ? GeometryCreateInfo::PositionPlanarU32() : GeometryCreateInfo::PlanarU32();
}
// clang-format off
Expand Down Expand Up @@ -1465,6 +1478,13 @@ ppx::Result GltfLoader::LoadMeshData(
targetGeometry.AppendIndex(*pGltfIndex);
}
}
// UINT8
else if (batch.indexFormat == grfx::FORMAT_R8_UINT) {
const uint8_t* pGltfIndex = static_cast<const uint8_t*>(pGltfIndices);
for (cgltf_size i = 0; i < pGltfAccessor->count; ++i, ++pGltfIndex) {
targetGeometry.AppendIndex(*pGltfIndex);
}
}
}
}

Expand Down

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