GLSL 纹理布局

Question

矩阵的布局（行优先与列优先）如何影响它创建的 GLSL 纹理？对该纹理的访问是否在着色器中发生变化？如果是列优先矩阵，我应该先将矩阵更改为行优先矩阵，然后将其作为纹理上传到 GPU 吗？

Answer 1

参见The OpenGL Shading Language 4.6, 5.4.2 Vector and Matrix Constructors, page 101：

To initialize a matrix by specifying vectors or scalars, the components are assigned to the matrix elements in column-major order.
mat4(float, float, float, float,  // first column
     float, float, float, float,  // second column
     float, float, float, float,  // third column
     float, float, float, float); // fourth column

这意味着如果您将矩阵 (mat4) 存储在 2 维 4*N、RGBA 纹理的行中，如下所示：

         0           1           2           3
mat4 m0  m0[0].xyzw  m0[1].xyzw  m0[2].xyzw  m0[3].xyzw
mat4 m1  m1[0].xyzw  m1[1].xyzw  m1[2].xyzw  m1[3].xyzw
mat4 m2  m2[0].xyzw  m2[1].xyzw  m2[2].xyzw  m2[3].xyzw
mat4 m3  .....

mat4 matArray[N]; // possibly std::vector<glm::mat4>( N );

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, 4, N, 0, GL_RGBA, GL_FLOAT, matArray);

然后您可以像这样从着色器中的纹理读取矩阵：

uniform sampler2D matSampler; 

void main()
{
    mat4 m0 = mat4(
        texelFetch( matSampler, ivec(0, 0), 0),
        texelFetch( matSampler, ivec(1, 0), 0),
        texelFetch( matSampler, ivec(2, 0), 0),
        texelFetch( matSampler, ivec(3, 0), 0) );

    mat4 m1 = mat4(
        texelFetch( matSampler, ivec(0, 1), 0),
        texelFetch( matSampler, ivec(1, 1), 0),
        texelFetch( matSampler, ivec(2, 1), 0),
        texelFetch( matSampler, ivec(3, 1), 0) );

   .....      
}

GLSL 纹理布局

GLSL texture layout

opengl

textures

glsl