how to read back RenderBuffer back to CPU;

[will mi]

I try to use renderbuffer instead of Texture to do off-screen
rendering.
While use Texture get the right result, but renderbuffer get a error
when use glReadPixels to read data of renderbuffer back to CPU.
The error is that "access violation writing location" .

I have malloc enough memory on CPU, and glGetTexImage works fine while
using Texture.
The funciotn of Texture, toImage3() gives me right Image, too.

So, how to use renderbuffer?( as I use rendering result on CPU, so
it's better to use renderbuffer, rather than Texture for me)

I use G3D-8.00-b1, Windows7, and GPU is NVIDIA GT240M.

following is main code of framebuffer.

My define:
FrameBuffer::Ref framebuffer;
Texture::Ref outColorTex;
Texture::Ref outColorTex2;
Renderbuffer::Ref renb;
Renderbuffer::Ref renb2;

init:
framebuffer = Framebuffer::create("framebuffer");
outColorTex = Texture::createEmpty("outColorTex", 1024, 1024,
ImageFormat::RGBA16());
outColorTex2 = Texture::createEmpty("outColorTex", 1024, 1024,
ImageFormat::RGBA16());
renb = RenderBuffer::createEmpty("renderbuffer", 1024, 1024,
ImageFormat::RGBA16F());
renb2 = RenderBuffer::createEmpty("renderbuffer2", 1024, 1024,
ImageFormat::RGBA16F());
framebuffer->set(FrameBuffer::COLOR_ATTACHMENT0, outColorTex);
framebuffer->set(Framebuffer::COLOR_ATTACHMENT1, outColorTex2);
//framebuffer->set(FrameBuffer::COLOR_ATTACHMENT0, renb);
//framebuffer->set(Framebuffer::COLOR_ATTACHMENT1, renb2);

render:
rd->pushState(framebuffer);
rd->push2D();
// Enable the shader
configureShaderArgs(localLighting);
//link a shader here and it will write gl_FragData[0]
and gl_FragData[1]
rd->setShader(testShader);

// Send model geometry to the graphics card
Draw::rect2D( framebuffer->rect2DBounds(), rd, Color3::green() );

float* cpuImage1 = new float[framebuffer->width() * framebuffer-
>height()];
float* cpuImage2 = new float[framebuffer->width() * framebuffer-
>height()];
glReadBuffer( GL_COLOR_ATTACHMENT0_EXT );
glReadPixels(0, 0, framebuffer->width(), framebuffer->height(),
GL_RGBA, GL_FLOAT, (GLvoid*)cpuImage1);
//glGetTexImage(GL_TEXTURE_RECTANGLE_ARB, 0, GL_RGBA, GL_FLOAT,
cpuImage1);
delete[] cpuImage1;
delete[] cpuImage2;

rd->pop2D();
rd->popState();

[will mi]

I find the stupid mistake I make;

float* cpuImage1 = new float[framebuffer->width() *
framebuffer->height()];

I forget to multiply it by 4, where each color has RGBA, 4 components;

float* cpuImage1 = new float[framebuffer->width() *

framebuffer->height() * 4];

Sorry for all!

[Corey Taylor]

You can hard-code it to 4-bytes per pixel, or you could try to use ImageFormat with the appropriate RGBA format.  Then, you should have access to the bits per pixel values.

 

corey