Opengles 2.0 multiple line colors

[MikeGomez]

I've posted to Stackoverflow and no one answers, and I've signed up for Khronos but it won't let me open a new thread for a question, so I was hoping maybe someone here knows something about opengl es 2.0.

I've searched the internet for about a week now and ran into a lot of promising leads but nothing works out so I need some feedback on my own code instead. Thanks.

I'm currently using Eclipse ADT for Android target.

I'm able to get several thousand lines on the the screen and I am happy with that. The problem is I can't figure how how to make each line a different color. Here is the current working code.

...
static float LineCoords[]	= new float [3 * 2 * MAX_LINE_LIST];
static float color[][] = new float [MAX_LINE_LIST][4];
static ByteBuffer bb;   
... 
	public void draw2(float[] mvpMatrix) {
	    // Add program to OpenGL ES environment
	    GLES20.glUseProgram(mProgram);
	    // get handle to vertex shader's vPosition member
	    mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");
	
	    // Enable a handle to the line vertices
	    GLES20.glEnableVertexAttribArray(mPositionHandle);
	
	    // get handle to fragment shader's vColor member
	    mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");
	    
	    // get handle to shape's transformation matrix
	    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
	    GLES20Renderer.checkGlError("glGetUniformLocation");
	
	    // Apply the projection and view transformation
	    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);
	    GLES20Renderer.checkGlError("glUniformMatrix4fv");
	    
	    if(g_NumLineList > 0)
	    {
	    	Bufferptr.put(LineCoords);
	      	Bufferptr.position(0);
		// Prepare the prim coordinate data
		 GLES20.glVertexAttribPointer(mPositionHandle, (COORDS_PER_VERTEX),
		                                 GLES20.GL_FLOAT, false, 0, Bufferptr); 		
		 // Set color for drawing the line
		 GLES20.glUniform4fv(mColorHandle, 1, color[0], 0); 
                          // Draw with 2 verts per line
		 GLES20.glDrawArrays(GLES20.GL_LINES, 0, 2 * g_NumLineList);
	    }    
  
	    // Disable vertex array
	    GLES20.glDisableVertexAttribArray(mPositionHandle);

	}
}

...
    private final String vertexShaderCode =
            // This matrix member variable provides a hook to manipulate
            // the coordinates of the objects that use this vertex shader
            "uniform mat4 uMVPMatrix;" +
            "attribute vec4 vPosition;" +
            "void main() {" +
            // The matrix must be included as a modifier of gl_Position.
            // Note that the uMVPMatrix factor *must be first* in order
            // for the matrix multiplication product to be correct.
            "  gl_Position = uMVPMatrix * vPosition;" +
            "}";

    private final String fragmentShaderCode =
            "precision mediump float;" +
            "uniform vec4 vColor;" +
            "void main() {" +
            "  gl_FragColor = vColor;" +
            "}";

...

 

[MikeGomez]

Ok, I have now been able to post to the OpenGL Khronos forum, but in the mean time I still need help.

The best lead I think I have is that there is some way to tell the vertex shader and the fragment shader to use colors per vertex, but I don't know how to make the changes to the rest of the code such as the draw code...

GLES20.glVertexAttribPointer(mPositionHandle, (COORDS_PER_VERTEX), GLES20.GL_FLOAT, false, 0, Bufferptr);
// Set color for drawing the line
GLES20.glUniform4fv(mColorHandle, 1, color[0], 0);
GLES20.glDrawArrays(GLES20.GL_LINES, 0, 2 * g_NumLineList); // 2 verts per line