I've modified the OpenGL es 2.0 template in Xcode to render that little box to an offscreen texture (50*50), then reset the view port and render the texture to the screen using a fullscreen quad. But the FPS dropped down so much that obvious lags were seen (about 10).
I know iPad has problems concerning fillrate, but this just doesn't seem right. I used only one FBO and changed its color attachment between texture and renderBuffer in the loop. Does this have any influence?
Besides, I was writing an audio visualizer (like the one in Windows Media Player) editing pixel values in OpenGL. Any suggestions?
here goes the code:
//implement the texture in -(id)init
glGenTextures(1, &ScreenTex);
glBindTexture(GL_TEXTURE_2D, ScreenTex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texSize, texSize, 0, GL_RGB, GL_UNSIGNED_BYTE, nil);
//And in the render loop
//draw to the texture
glViewport(0, 0, texSize, texSize);
glBindTexture(GL_TEXTURE_2D, ScreenTex);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, ScreenTex, 0);
glClear(GL_COLOR_BUFFER_BIT);
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
glUniform1i(Htunnel, 0);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
//switch to render to render buffer here
glViewport(0, 0, backingWidth, backingHeight);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER,colorRenderbuffer);
glClear(GL_COLOR_BUFFER_BIT);
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, texVertices);
glUniform1i(Htunnel, 1);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
//vertex shader
void main()
{
if (tunnel==0) {
gl_Position = position;
gl_Position.y += sin(translate) / 2.0;
colorVarying = color;
}else {
f_texCoord = v_texCoord;
gl_Position = position;
}
}
//frag shader
void main()
{
if (tunnel==0) {
gl_FragColor = colorVarying;
} else {
gl_FragColor = texture2D(s_texture, f_texCoord);
}
}
