Writing values to a GLSL uniform array element with offset

Question

I am trying to find a way to set the value of a single element within an array of vec3's. All I can find are ways to write the whole array or a few elements from the start. The problem is that I can't find a way to offset the "address" it's writing to ( I am used to C++ ).

The reason I want to do this is that I have an array of lights with certain variables in my fragment shader. But I want to flag my light's dirty and only send new data to the shader when it has been changed. So when I change light number 4's position, I want to change u_LightPos[3] value.

Fragment Shader:

const int MAX_LIGHTS = 6;
uniform vec3 u_LightPos[MAX_LIGHTS];

OpenGL ES 2.0 (Java, android platform ):

int LightPos = GLES20.glGetUniformLocation(ShaderProgram, "u_LightPos");
GLES20.glUniform3fv(LightPos, 3, m_aLightPos, 0 );

The glUniform3fv function does have a count and offset parameter, but the offset is used for the offset of the array you are reading from, not the shader's array you are writing to.

Dr. Snoopy · Accepted Answer · 2014-03-12 09:59:37Z

2

You can do this:

int loc = GLES20.glGetUniformLocation(ShaderProgra, "u_LightPos[3]");
GLES20.glUniform3fv(LightPos, 3, m_aLightPos, 0 );

Each element of the array has a individual location, and this applies to structs as well. You can read more about this here

answered Mar 12, 2014 at 9:59

Dr. Snoopy

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