OpenGL isn't setting the divisor correctly. Shader transforms vertices instead of meshes

OpenGL OpenGL: Advanced Coding
1

I was trying to enable instanced rendering of a mesh. I extracted the relevant code snippets. I did some debugging and it’s seems that the instanced position data transforms the vertices instead of each individual mesh. Which makes me believe that OpenGL is setting the divisor for second buffer as zero instead of one. I tried everything but can’t seem to understand why this is happening. Appreciate any help.

//load first vertex buffer

index = 0;
size = 3;
offset = 0;
bindingIndex = 0;
glVertexArrayAttribFormat(mVao, index, size, GL_FLOAT, GL_FALSE, offset);
glEnableVertexArrayAttrib(mVao, index);
glVertexArrayAttribBinding(mVao, index, bindingIndex);

//load second buffer for instancing using vec3 positions

index = 10;
size = 3;
offset = 0;
bindingIndex = 1;
glVertexArrayAttribFormat(mVao, index, size, GL_FLOAT, GL_FALSE, offset);
glEnableVertexArrayAttrib(mVao, index);
glVertexArrayAttribBinding(mVao, index, bindingIndex);

glVertexArrayBindingDivisor(mVao, index, 1);

Vertex shader

layout (location = 0) in vec3 v_in_pos;
layout (location = 10) in vec3 v_in_inst_pos;
uniform mat4 u_M = mat4(1);
uniform mat4 u_PV = mat4(1);
void main() {
   gl_Position = u_PV*u_M*vec4(v_in_inst_pos+v_in_pos, 1.0);
}
2

You are confusing your indices.

The instance divisor applies to the buffer binding index, not the vertex attribute index. That means it applies equally to all attributes which use that buffer binding.

So in this code, it should not be index; it should be bindingIndex.

1 Like
3

After wasting so much time on this, this finally fixed it, thank you very much!