CODEWITHSUNDEEP
androidopengl-esvbo
Derek
Derek

Reputation: 43

Using VBOs/IBOs in OpenGL ES 2.0 on Android

I am trying to create a simple test program on android (API 10) using OpenGL ES 2.0 to draw a simple rectangle. I can get this to work with float buffers referencing the vertices directly, but i would rather do it with VBOs/IBOs. I have looked for countless hours trying to find a simple explanation (tutorial), but have yet to come across one. My code compiles and runs just fine, but nothing is showing up on the screen other than the clear color.

Here are some code chunks to help explain how I have it set up right now.

Part of onSurfaceChanged():

int[] buffers = new int[2];
GLES20.glGenBuffers(2, buffers, 0);
rectVerts = buffers[0];
rectInds = buffers[1];
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, rectVerts);
GLES20.glBufferData(GLES20.GL_ARRAY_BUFFER, (rectBuffer.limit()*4), rectBuffer, GLES20.GL_STATIC_DRAW);

GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, rectInds);
GLES20.glBufferData(GLES20.GL_ELEMENT_ARRAY_BUFFER, (rectIndices.limit()*4), rectIndices, GLES20.GL_STATIC_DRAW);

Part of onDrawFrame():

GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, rectVerts);
GLES20.glEnableVertexAttribArray(0);
GLES20.glVertexAttribPointer(0, 3, GLES20.GL_FLOAT, false, 0, 0);
GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, rectInds);
GLES20.glDrawElements(GLES20.GL_TRIANGLES, 6, GLES20.GL_INT, 0);

Upvotes: 3

Views: 5140

Answers (1)

Tim
Tim

Reputation: 35943

I don't see anything immediately wrong, but here's some ideas you can touch on.

1) 'Compiling and running fine' is a useless metric for an opengl program. Errors are reported through actively calling glGetError and checking compile and link status of the shaders with glGet(Shader|Program)iv. Do you check for errors anywhere?

2) You shouldn't be assuming that 0 is the correct index for vertices. It may work now but will likely break later if you change your shader. Get the correct index with glGetAttribLocation.

3) You're binding the verts buffer onDraw, but I don't see anything about the indices buffer. Is that always bound?

4) You could also try drawing your VBO with glDrawArrays to get the index buffer out of the equation, just to help debugging to see which part is wrong.

Otherwise what you have looks correct as far as I can tell in that small snippet. Maybe something else outside of it is going wrong.

Upvotes: 3

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