CODEWITHSUNDEEP
androidgraphicsopengl-es
farm ostrich
farm ostrich

Reputation: 5949

OpenGL (ES) -- Storing and using a color array in a VBO, and applying it to a VBO triangle

How can this be done? This code isn't working:


//////////INIT COLOR VBO FOR USE WITH A TRIANGLE    
triColorBuffer = ByteBuffer.allocateDirect(3 * 4
    * 4).order(ByteOrder.nativeOrder()).asFloatBuffer();        

float[] colors = { 
1f, 0f, 0f, 1f,
0f, 1f, 0f, 1f, 
0f, 0f, 1f, 1f,};

triColorBuffer.put(colors);
triColorBuffer.flip();
int[] buffer = new int[1];
gl11.glGenBuffers(1, buffer, 0);
colorPointerTri = buffer[0];
gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, colorPointerTri);
gl11.glBufferData(GL11.GL_ARRAY_BUFFER, triColorBuffer.capacity() 
    * 4, triColorBuffer, GL11.GL_STATIC_DRAW);

////////////DRAW USING COLOR VBO
gl11.glEnableClientState(GL10.GL_COLOR_ARRAY);
gl11.glEnableClientState(GL10.GL_VERTEX_ARRAY);
gl11.glPushMatrix();

gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, vertexPointerTri);
gl11.glBindBuffer(GL11.GL_ELEMENT_ARRAY_BUFFER, indexPointerTri);
gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, colorPointerTri);
gl11.glColorPointer(4, GL10.GL_FLOAT, 0, 0);
gl11.glVertexPointer(3, GL10.GL_FLOAT, 0, 0);
gl11.glDrawElements(GL10.GL_TRIANGLES, 3, GL10.GL_UNSIGNED_SHORT, 0);
gl11.glDisableClientState(GL10.GL_COLOR_ARRAY);
gl11.glDisableClientState(GL10.GL_VERTEX_ARRAY);

gl11.glPopMatrix();
gl11.glDisableClientState(GL10.GL_COLOR_ARRAY);
gl11.glDisableClientState(GL10.GL_VERTEX_ARRAY);
gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, 0);
gl11.glBindBuffer(GL11.GL_ELEMENT_ARRAY_BUFFER, 0);

The triangle draws VBO'd or nor, and the color gradient (glcolorpointer) works non VBO'd, but I can't get the VBO'd triangle to color using a color pointer (VBO or without). Help Appreciated.

Upvotes: 0

Views: 2865

Answers (2)

Christian Rau
Christian Rau

Reputation: 45948

You are binding the vertex buffer and right after that you bind the color buffer. When you now call glColor/VertexPointer, both colors and vertices are sourced from the color buffer. You need to write:

gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, vertexPointerTri);
gl11.glVertexPointer(3, GL10.GL_FLOAT, 0, 0);
gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, colorPointerTri);
gl11.glColorPointer(4, GL10.GL_FLOAT, 0, 0);

As the gl...Pointer command uses the buffer that is currently bound.

Upvotes: 3

harism
harism

Reputation: 6073

Please do correct me if I'm wrong, I started out with VBOs just 15mins ago.

Anyway, it seems so you have to use VBOs 'in two'. First you bind your data/array, and right after that tell GL context what you just gave it. Took me a good a while to read through this source file to figure out what was going on and truly hope I didn't misunderstood it totally. Excerpt from that file;

if (useTexture) {
    gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, mTextureCoordBufferIndex);
    gl11.glTexCoordPointer(2, mCoordinateType, 0, 0);
}            
if (useColor) {
    gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, mColorBufferIndex);
    gl11.glColorPointer(4, mCoordinateType, 0, 0);
}

In your code, you're binding 3 times and right after start switching what was binded. I don't know what exactly happens there but I would give it a go to try e.g.

gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, vertexPointerTri);
gl11.glVertexPointer(3, GL10.GL_FLOAT, 0, 0);
gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, colorPointerTri);
gl11.glColorPointer(4, GL10.GL_FLOAT, 0, 0);
gl11.glBindBuffer(GL11.GL_ELEMENT_ARRAY_BUFFER, indexPointerTri);
gl11.glDrawElements(GL10.GL_TRIANGLES, 3, GL10.GL_UNSIGNED_SHORT, 0);

Also from what I've seen it shouldn't do any harm if you unbind your arrays after rendering. Maybe it's in your code not copy/pasted here, but just in case.

gl11.glBindBuffer(GL11.GL_ARRAY_BUFFER, 0);
gl11.glBindBuffer(GL11.GL_ELEMENT_ARRAY_BUFFER, 0);

Upvotes: 3

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