我正在制作一个在 WGPU (Vulkan GLSL) 计算着色器中计算切线和双切线的教程。我正在用我在搅拌机中制作的 .obj 在 CPU 上创建顶点缓冲区。
这是计算着色器的代码。
#version 450
#define VERTICES_PER_TRIANGLE 3
layout(local_size_x = VERTICES_PER_TRIANGLE) in;
// Should match the struct in model.rs
struct ModelVertex {
vec3 position;
vec2 tex_coords;
vec3 normal;
vec3 tangent;
vec3 bitangent;
};
layout(std140, set=0, binding=0) buffer SrcVertexBuffer {
ModelVertex srcVertices[];
};
layout(std140, set=0, binding=1) buffer DstVertexBuffer {
ModelVertex dstVertices[];
};
layout(std140, set=0, binding=2) buffer IndexBuffer {
uint Indices[];
};
void main() {
uint index = gl_GlobalInvocationID.x;
// Grab the indices for the triangle
uint i0 = Indices[index];
uint i1 = Indices[index + 1];
uint i2 = Indices[index + 2];
// Grab the vertices for the triangle
ModelVertex v0 = srcVertices[i0];
ModelVertex v1 = srcVertices[i1];
ModelVertex v2 = srcVertices[i2];
// Grab the position and uv components of the vertices
vec3 pos0 = v0.position;
vec3 pos1 = v1.position;
vec3 pos2 = v2.position;
vec2 uv0 = v0.tex_coords;
vec2 uv1 = v1.tex_coords;
vec2 uv2 = v2.tex_coords;
// Calculate the edges of the triangle
vec3 delta_pos1 = pos1 - pos0;
vec3 delta_pos2 = pos2 - pos0;
// This will give us a direction to calculate the
// tangent and bitangent
vec2 delta_uv1 = uv1 - uv0;
vec2 delta_uv2 = uv2 - uv0;
// Solving the following system of equations will
// give us the tangent and bitangent.
// delta_pos1 = delta_uv1.x * T + delta_u.y * B
// delta_pos2 = delta_uv2.x * T + delta_uv2.y * B
// Luckily, the place I found this equation provided
// the solution!
float r = 1.0 / (delta_uv1.x * delta_uv2.y - delta_uv1.y * delta_uv2.x);
vec3 tangent = (delta_pos1 * delta_uv2.y - delta_pos2 * delta_uv1.y) * r;
vec3 bitangent = (delta_pos2 * delta_uv1.x - delta_pos1 * delta_uv2.x) * r;
// We'll use the same tangent/bitangent for each vertex in the triangle
dstVertices[i0].tangent = tangent;
dstVertices[i1].tangent = tangent;
dstVertices[i2].tangent = tangent;
dstVertices[i0].bitangent = bitangent;
dstVertices[i1].bitangent = bitangent;
dstVertices[i2].bitangent = bitangent;
}
这导致如下图所示。
问题出现在最后六行。
dstVertices[i0].tangent = tangent;
dstVertices[i1].tangent = tangent;
dstVertices[i2].tangent = tangent;
dstVertices[i0].bitangent = bitangent;
dstVertices[i1].bitangent = bitangent;
dstVertices[i2].bitangent = bitangent;
如果我删除这些行，则输出很好（尽管由于切线和双切线是 0 向量，所以照明都错了）。
为什么修改切线和双切线会弄乱顶点的位置？
这是上下文的其余代码。https://github.com/sotrh/learn-wgpu/tree/compute/code/intermediate/tutorial14-compute
编辑：
这是我调用计算着色器的代码。
let src_vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
label: Some(&format!("{:?} Vertex Buffer", m.name)),
contents: bytemuck::cast_slice(&vertices),
// UPDATED!
usage: wgpu::BufferUsage::STORAGE,
});
let dst_vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
label: Some(&format!("{:?} Vertex Buffer", m.name)),
contents: bytemuck::cast_slice(&vertices),
// UPDATED!
usage: wgpu::BufferUsage::VERTEX | wgpu::BufferUsage::STORAGE,
});
let index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
label: Some(&format!("{:?} Index Buffer", m.name)),
contents: bytemuck::cast_slice(&m.mesh.indices),
// UPDATED!
usage: wgpu::BufferUsage::INDEX | wgpu::BufferUsage::STORAGE,
});
let binding = BitangentComputeBinding {
dst_vertex_buffer,
src_vertex_buffer,
index_buffer,
num_elements: m.mesh.indices.len() as u32,
};
// Calculate the tangents and bitangents
let calc_bind_group = self.binder.create_bind_group(
&binding,
device,
Some("Mesh BindGroup")
);
let mut encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
label: Some("Tangent and Bitangent Calc"),
});
{
let mut pass = encoder.begin_compute_pass();
pass.set_pipeline(&self.pipeline);
pass.set_bind_group(0, &calc_bind_group, &[]);
pass.dispatch(binding.num_elements as u32 / 3, 1, 1);
}
queue.submit(std::iter::once(encoder.finish()));
device.poll(wgpu::Maintain::Wait);
着色器应该循环遍历网格中的所有三角形，并使用该三角形顶点的位置和 uv 坐标计算切线和双切线。我猜测与多个三角形共享的顶点同时被写入，导致这种内存损坏。
我不认为这是其他地方的着色器的问题，因为我对光使用相同的模型，而负责该模型的顶点着色器根本不使用切线和双切线。
#version 450
layout(location=0) in vec3 a_position;
layout(location=0) out vec3 v_color;
layout(set=0, binding=0)
uniform Uniforms {
vec3 u_view_position;
mat4 u_view_proj;
};
layout(set=1, binding=0)
uniform Light {
vec3 u_position;
vec3 u_color;
};
// Let's keep our light smaller than our other objects
float scale = 0.25;
void main() {
vec3 v_position = a_position * scale + u_position;
gl_Position = u_view_proj * vec4(v_position, 1);
v_color = u_color;
}
查看 Render Doc 中的顶点数据表明它们的位置数据变得混乱。
如果我将切线和副切线设置为 ，这也是立方体的样子vec3(0, 1, 0)。
我唯一的猜测是存储缓冲区有一个我不知道的字节对齐规则。我知道统一缓冲区就是这种情况，但是我将存储缓冲区用于我的实例化代码，这似乎没有任何问题。
