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Simplified dynamic alignment calculation

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Fixes #381
This commit is contained in:
saschawillems 2017-10-27 22:03:21 +02:00
parent 19245a0f51
commit 5107cf3ed0
2 changed files with 13 additions and 7 deletions
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9
dynamicuniformbuffer/README.md
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@ -48,9 +48,12 @@ First step is to calculate the alignment required for the data we want to store
```cpp ```cpp
void prepareUniformBuffers() void prepareUniformBuffers()
{ {
// Calculate required alignment depending on device limits // Calculate required alignment based on minimum device offset alignment
size_t uboAlignment = vulkanDevice->properties.limits.minUniformBufferOffsetAlignment; size_t minUboAlignment = vulkanDevice->properties.limits.minUniformBufferOffsetAlignment;
dynamicAlignment = (sizeof(glm::mat4) / uboAlignment) * uboAlignment + ((sizeof(glm::mat4) % uboAlignment) > 0 ? uboAlignment : 0); dynamicAlignment = sizeof(glm::mat4);
if (minUboAlignment > 0) {
dynamicAlignment = (dynamicAlignment + minUboAlignment - 1) & ~(minUboAlignment - 1);
}
``` ```
The max. allowed alignment (as per spec) is 256 bytes which may be much higher than the data size we actually need for each entry (one 4x4 matrix = 64 bytes). The max. allowed alignment (as per spec) is 256 bytes which may be much higher than the data size we actually need for each entry (one 4x4 matrix = 64 bytes).

11
dynamicuniformbuffer/dynamicuniformbuffer.cpp
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@ -410,16 +410,19 @@ public:
// Allocate data for the dynamic uniform buffer object // Allocate data for the dynamic uniform buffer object
// We allocate this manually as the alignment of the offset differs between GPUs // We allocate this manually as the alignment of the offset differs between GPUs
// Calculate required alignment depending on device limits // Calculate required alignment based on minimum device offset alignment
size_t uboAlignment = vulkanDevice->properties.limits.minUniformBufferOffsetAlignment; size_t minUboAlignment = vulkanDevice->properties.limits.minUniformBufferOffsetAlignment;
dynamicAlignment = (sizeof(glm::mat4) / uboAlignment) * uboAlignment + ((sizeof(glm::mat4) % uboAlignment) > 0 ? uboAlignment : 0); dynamicAlignment = sizeof(glm::mat4);
if (minUboAlignment > 0) {
dynamicAlignment = (dynamicAlignment + minUboAlignment - 1) & ~(minUboAlignment - 1);
}
size_t bufferSize = OBJECT_INSTANCES * dynamicAlignment; size_t bufferSize = OBJECT_INSTANCES * dynamicAlignment;
uboDataDynamic.model = (glm::mat4*)alignedAlloc(bufferSize, dynamicAlignment); uboDataDynamic.model = (glm::mat4*)alignedAlloc(bufferSize, dynamicAlignment);
assert(uboDataDynamic.model); assert(uboDataDynamic.model);
std::cout << "minUniformBufferOffsetAlignment = " << uboAlignment << std::endl; std::cout << "minUniformBufferOffsetAlignment = " << minUboAlignment << std::endl;
std::cout << "dynamicAlignment = " << dynamicAlignment << std::endl; std::cout << "dynamicAlignment = " << dynamicAlignment << std::endl;
// Vertex shader uniform buffer block // Vertex shader uniform buffer block