Incomplete rendering to FBO/texture --> file

Hello

 I) I set an FBO and texture this way:
int[] p = new int[1];
gl.glGenFramebuffers(1, p, 0);
mFbo = p[0];
gl.glBindFramebuffer(GL2GL3.GL_FRAMEBUFFER, mFbo);

// create rendering texture
gl.glGenTextures(1, p, 0);
mTexture = p[0];
gl.glBindTexture(GL2GL3.GL_TEXTURE_2D, mTexture);
gl.glTexParameteri(GL2GL3.GL_TEXTURE_2D, GL2GL3.GL_TEXTURE_MIN_FILTER, GL2GL3.GL_LINEAR);
gl.glTexParameteri(GL2GL3.GL_TEXTURE_2D, GL2GL3.GL_TEXTURE_MAG_FILTER, GL2GL3.GL_LINEAR);
gl.glTexParameteri(GL2GL3.GL_TEXTURE_2D, GL2GL3.GL_TEXTURE_WRAP_S, GL2GL3.GL_CLAMP_TO_EDGE);
gl.glTexParameteri(GL2GL3.GL_TEXTURE_2D, GL2GL3.GL_TEXTURE_WRAP_T, GL2GL3.GL_CLAMP_TO_EDGE);
gl.glTexImage2D(GL2GL3.GL_TEXTURE_2D, 0, GL2GL3.GL_RGBA, mWidth, mHeight, 0, GL2GL3.GL_RGBA, GL2GL3.GL_UNSIGNED_BYTE, null);
gl.glBindTexture(GL2GL3.GL_TEXTURE_2D, 0);

// associate the texture as the rendering buffer for the whiteboard framebuffer
gl.glFramebufferTexture2D(GL2GL3.GL_FRAMEBUFFER, GL2GL3.GL_COLOR_ATTACHMENT0, GL2GL3.GL_TEXTURE_2D, whiteboardRenderTexture, 0);

// create VBO to hold vertices
gl.glGenBuffers(1, p, 0);
mVBO = p[0];
gl.glBindBuffer(GL2GL3.GL_ARRAY_BUFFER, mVBO);

// check FBO status
if(gl.glCheckFramebufferStatus(GL2GL3.GL_FRAMEBUFFER) != GL2GL3.GL_FRAMEBUFFER_COMPLETE) {
    System.out.println("Failed to complete whiteboard framebuffer object creation:" + gl.glCheckFramebufferStatus(GL2GL3.GL_FRAMEBUFFER));
    return;
}
gl.glBindFramebuffer(GL2GL3.GL_FRAMEBUFFER, 0);

II)  I try to draw a simple triangle to the FBO and its bound texture:
 float vertices[] = { -0.5f, -0.5f, 0.5f, -0.5f, 0.0f, 0.5f };
 int vertexCount = 3;
FloatBuffer verticesBuffer = FloatBuffer.wrap(vertices);
verticesBuffer.position(0);

gl.glBindFramebuffer(GL2GL3.GL_FRAMEBUFFER, mFbo);
gl.glClearColor(rand.nextFloat(), rand.nextFloat(), rand.nextFloat(), 1.0f);
gl.glClear(GL2GL3.GL_COLOR_BUFFER_BIT);

gl.glBufferData(GL2GL3.GL_ARRAY_BUFFER, vertexCount, verticesBuffer, GL2GL3.GL_DYNAMIC_DRAW); // populate the VBO with the actual vertices to be drawn

gl.glUseProgram(mDrawProgram);
gl.glEnableVertexAttribArray(pointAttributeLocation);
gl.glVertexAttribPointer(pointAttributeLocation, kVertexDimensions, GL2GL3.GL_FLOAT, false, kVertexStride, 0);
gl.glGetError();

gl.glViewport(0, 0, mWidth, mHeight);
gl.glDrawArrays(GL2GL3.GL_TRIANGLES, 0, vertexCount);
gl.glGetError();
gl.glBindFramebuffer(GL2GL3.GL_FRAMEBUFFER, 0);

III) I save everything to some file:
gl.glBindFramebuffer(GL2GL3.GL_FRAMEBUFFER, mFbo);
ByteBuffer buffer = ByteBuffer.allocateDirect(mWidth * mHeight * 4);
BufferedImage image = new BufferedImage(mWidth, mHeight, BufferedImage.TYPE_INT_ARGB);
gl.glReadBuffer(GL2GL3.GL_COLOR_ATTACHMENT0);
gl.glReadPixels(0, 0, mWidth, mHeight, GL2GL3.GL_RGBA, GL2GL3.GL_UNSIGNED_BYTE, buffer);
gl.glGetError();
for (int w = 0; w < mWidth; w++) {
    for (int h = 0; h < mHeight; h++) {
        int i = (w + (mWidth * h)) * 4;
        int r = buffer.get(i) & 0xFF;
        int g = buffer.get(i + 1) & 0xFF;
        int b = buffer.get(i + 2) & 0xFF;
        int a = buffer.get(i + 3) & 0xFF;
        image.setRGB(w, h, (a << 24) | (r << 16) | (g << 8) | b);
    }
}
try {
    ImageIO.write(image, "png", new File(SAVED_IMAGES_FILES_PATH+”/whatever.png“));
} catch (IOException ex) { ex.printStackTrace(); }
gl.glBindFramebuffer(GL2GL3.GL_FRAMEBUFFER, 0);

IV) I use those basic shaders

#version 330 core

in vec2 point;
void main() {
    gl_Position = vec4(point.x, point.y, 0.0, 1.0);
}

and

#version 330 core

out vec4 color;
void main() {
    color = vec4(1.0f, 0.0f, 0.0f, 1.0f);
}

Result :  I can see in the png file that the background set by clearColor is changing each time I execute, so something is actually written in the texture, and then to the file. But the triangle itself never appears in the file.

Can somebody point out what I am missing in my FBO/texture rendering ?
Thank you

Hi

Have you looked at our unit tests?

I looked at the demo Cubefbo. The use of FBOject alleviates the framebuffer generation and texture binding, so I'm using it now, but I dont see how this could be the issue. Cubefbo uses GL2 and glVertexPointer function. Unfortunately, my environment does not seem to allow me the use of GL2 (GL2GL3 instead), so I'm still using glVertexAttribPointer, where the issue in my code seems to lie somehow.

Which other demo would you recommend to check ? Thank you.

As per your recommendation I have been looking closer to your demos and tests, and have played a bit with the tests suite Offscreen + RawGL2ES2demo : those 2 seem very promising for what I need. I now have to look deeper into the magic inside !
Thanks.