opengl : loading array types to uniform buffer objects

Question

Here is my uniform block in the fragment shader

layout (std140)   uniform Material
{
 float array[2];
};

Here is the Uniform Block Object . I am using LWJGL 2.9.3

  private UBO(int programID,String blockName)
  {
   blockID=GL31.glGetUniformBlockIndex(programID,blockName);  //Get index of uniform block
   
   IntBuffer indices=BufferUtils.createIntBuffer(16);
   GL31.glGetActiveUniformBlock(programID,blockID,GL31.GL_UNIFORM_BLOCK_ACTIVE_UNIFORM_INDICES,indices); //query all the indices of every variable in the uniform block
   indices.flip().limit(GL31.glGetActiveUniformBlocki(programID,blockID,GL31.GL_UNIFORM_BLOCK_ACTIVE_UNIFORMS)); //the above method requires an int buffer of 16 even if i dont have 16 variables, but after retriving indices limit the buffer to read only actual number of variables
   while(indices.hasRemaining())
   {
    int variableIndex=indices.get();
   
    String name=GL31.glGetActiveUniformName(programID
                                           ,variableIndex
                                           ,GL31.glGetActiveUniformsi(programID,variableIndex,GL31.GL_UNIFORM_NAME_LENGTH)); //get the name of the variable
    
    int offset=GL31.glGetActiveUniformsi(programID,variableIndex,GL31.GL_UNIFORM_OFFSET); //query the offset[will use it in buffer sub data]
   
    offsets.put(name,offset);
   }
   
   
   GL15.glBindBuffer(GL31.GL_UNIFORM_BUFFER,bufferID=GL15.glGenBuffers());
   
   GL15.glBufferData(GL31.GL_UNIFORM_BUFFER
                    ,GL31.glGetActiveUniformBlocki(programID,blockID,GL31.GL_UNIFORM_BLOCK_DATA_SIZE)
                    ,GL15.GL_DYNAMIC_DRAW); //allocate buffer to the actual size of the uniform block
   
   GL15.glBindBuffer(GL31.GL_UNIFORM_BUFFER,0);
  }
  
  private void bufferData(String name,Buffer value)
  { 
   int offset=offsets.get(name); //update float or int arrays
   if(value instanceof FloatBuffer){GL15.glBufferSubData(GL31.GL_UNIFORM_BUFFER,offset,(FloatBuffer)value);}
   else{GL15.glBufferSubData(GL31.GL_UNIFORM_BUFFER,offset,(IntBuffer)value);}
  }

With regular non array variables it works fine but with arrays the float and every array type values are loaded incorrectly. I have read the docs specifying that every element in the array has an 16[vec4 size] alignment but i don't know how to specify that in my code

to update the float array i simply use

bufferData("array[0]",BufferUtils.createFloatBuffer(2).put(new float[]{10.5f,3.0f}).flip());
//the array[0] dosen't actually refer to only the first element of the array it is the name of the array returned by GL31.glGetActiveUniformName()

but again the floats are all loaded incorrectly.

Rabbid76 Rabbid76 · Accepted Answer · 2020-12-05T16:51:04

I have read the docs specifying that every element in the array has an 16[vec4 size] alignment but i don't know how to specify that in my code [...]

You're right, you would have to add 3 floats for padding per element:

BufferUtils.createFloatBuffer(8).put(new float[]{10.5f,0.0f,0.0f,0.0f,3.0f,0.0f,0.0f,0.0f}).flip()

However, I recommend to use a single vec2 rather than float array[2]:

layout (std140)   uniform Material
{
    vec2 array;
};

Note, in GLSL the components of an vector data type can be accessed with Swizzling or the index operator (e.g. array[0] or array[1]).

opengl : loading array types to uniform buffer objects

1 Answers