Can't set uniform value in OpenGL shader
c++, glm-math, glsl, opengl
Solution
Are you calling `glUseProgram` before setting the uniforms? A full working listing can be found in many examples online, including what I had written sometime back (Github: `sgxperf/sgxperf_gles20_vg.cpp`) that shows the sequence to be:
glCreateProgram()
glAttachShader()
glLinkProgram()
glUseProgram()
glGetUniformLocation()
glUniformMatrix4fv()
Problem
I am trying to get simple shaders to work. To be more specific, I am trying to set a uniform value of the shader. The shaders compile successfully and work correctly if I eliminate the uniform value. Here is the (vertex) shader code: ``` #version 440 core layout(location = 0) in vec3 vertex; uniform mat4 mvp; void main() { gl_Position = mvp * vec4(vertex, 1); } ``` And the code I use to set the value (`glGetUniformLocation` returns 0 as expected): ``` mvp = glm::mat4( glm::vec4(3.0f, 0.0f, 0.0f, 0.0f), glm::vec4(0.0f, 1.0f, 0.0f, 0.0f), glm::vec4(0.0f, 0.0f, 1.0f, 0.0f), glm::vec4(0.0f, 0.0f, 0.0f, 2.0f) ); GLuint matrix = glGetUniformLocation(program, "mvp"); glUniformMatrix4fv(matrix, 1, GL_FALSE, glm::value_ptr(mvp)); ``` The problem is that it doesn't seem to set the value at all. If I query the uniform's value using `glGetUniformfv`, it returns the default value (not the one I just set), and the geometry doesn't show up at all (but that is just a consequence, that's not the problem here). If I hardcode the uniform's value in the shader, the application displays the geometry correctly, and when asked for the value (again, using `glGetUniformfv`), it returns the correct value. ``` #version 440 core layout(location = 0) in vec3 vertex; uniform mat4 mvp = mat4( vec4(1.0f, 0.0f, 0.0f, 0.0f), vec4(0.0f, 1.0f, 0.0f, 0.0f), vec4(0.0f, 0.0f, 1.0f, 0.0f), vec4(0.0f, 0.0f, 0.0f, 2.0f) ); void main() { gl_Position = mvp * vec4(vertex, 1); } ``` Any idea why does this happen? I am using OpenGL 4.4, but I have tried many different versions with the same result.