如何将帧缓冲区对象绘制到默认帧缓冲区

Question

此代码应该使用帧缓冲区对象和渲染缓冲区清除黄色背景，但我得到的是黑色背景。

#include <SDL2/SDL.h>
#include <GL/glew.h>

int main( int argc, char** argv)
    {
    SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 3);
    SDL_GL_SetAttribute( SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute( SDL_GL_ACCELERATED_VISUAL, 1);

    SDL_Window* gWindow= SDL_CreateWindow( "Title",
        SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
        500, 500, SDL_WINDOW_OPENGL);
    SDL_GLContext gContext= SDL_GL_CreateContext( gWindow);

    glewExperimental= GL_TRUE;
    glewInit();

    GLuint fbo;
    glGenFramebuffers( 1, &fbo);
    glBindFramebuffer( GL_FRAMEBUFFER, fbo);

    GLuint color_rbr;
    glGenRenderbuffers(1, &color_rbr);
    glBindRenderbuffer( GL_RENDERBUFFER, color_rbr);
    glRenderbufferStorage( GL_RENDERBUFFER, GL_RGBA32UI, 500, 500);
    glFramebufferRenderbuffer( GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, color_rbr);

    GLuint depth_rbr;
    glGenRenderbuffers( 1, &depth_rbr);
    glBindRenderbuffer( GL_RENDERBUFFER, depth_rbr);
    glRenderbufferStorage( GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, 500, 500);
    glFramebufferRenderbuffer( GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth_rbr);

    if( glCheckFramebufferStatus( GL_DRAW_FRAMEBUFFER)!= GL_FRAMEBUFFER_COMPLETE)
        return 1;
    if( glCheckFramebufferStatus( GL_READ_FRAMEBUFFER)!= GL_FRAMEBUFFER_COMPLETE)
        return 2;

    glViewport( 0, 0, 500, 500);
    glClearColor( 1, 1, 0, 0);
    SDL_GL_SetSwapInterval( 1);

    int quit= 0;
    SDL_Event event;
    glReadBuffer( GL_COLOR_ATTACHMENT0);

    while( !quit)
        {
        while( SDL_PollEvent( &event))
            if( event.type== SDL_QUIT)
                quit= 1;

        glBindFramebuffer( GL_DRAW_FRAMEBUFFER, fbo);
        glDrawBuffer( GL_COLOR_ATTACHMENT0);
        glClear( GL_COLOR_BUFFER_BIT);
        glBindFramebuffer( GL_DRAW_FRAMEBUFFER, 0);
        glDrawBuffer( GL_BACK);
        glBlitFramebuffer(
            0, 0, 500, 500,
            0, 0, 500, 500,
            GL_COLOR_BUFFER_BIT, GL_NEAREST);
        SDL_GL_SwapWindow( gWindow);
        }
    SDL_DestroyWindow( gWindow);
    return 0;
    }

它首先清除具有指定颜色的帧缓冲区对象，然后将帧缓冲区对象blits到默认帧缓冲区。代码有问题吗？我似乎找不到问题的确切位置。

Answer 1

glBlitFramebuffer 操作失败，因为读取缓冲区包含无符号整数值而默认帧缓冲区不包含。这会导致 GL_INVALID_OPERATION 错误。

读取缓冲区的格式为GL_RGBA32UI

glRenderbufferStorage( GL_RENDERBUFFER, GL_RGBA32UI, 500, 500);

而绘图缓冲区（默认帧缓冲区）的格式是无符号规范化整数格式（可能是GL_RGBA8）。

如果您将内部格式更改为 GL_RGBA16 或 GL_RGBA32F，您的代码将正常工作。

注意，RGBA8 和 RGBA16 等格式是规范化浮点格式，可以存储 [0.0, 1.0] 范围内的浮点值。
但是像RGBA16UI和RGBA32UI这样的格式是无符号整数格式，可以存储相应范围内的整数值。

规范说无符号整数值只能复制为无符号整数值。所以源格式必须是 *UI，目标格式也必须是 *UI。

参见 OpenGL 4.6 API Compatibility Profile Specification - 18.3.2 Blitting Pixel Rectangles 第 662 页：

void BlitFramebuffer( int srcX0, int srcY0, int srcX1, int srcY1, 
    int dstX0, int dstY0, int dstX1, int dstY1, bitfield mask, enum filter );
[...]

Errors

[...]

An INVALID_OPERATION error is generated if format conversions are not supported, which occurs under any of the following conditions:

The read buffer contains fixed-point or floating-point values and any draw buffer contains neither fixed-point nor floating-point values.

The read buffer contains unsigned integer values and any draw buffer does not contain unsigned integer values.

The read buffer contains signed integer values and any draw buffer does not contain signed integer values.

如何将帧缓冲区对象绘制到默认帧缓冲区

How to draw a framebuffer object to the default framebuffer

c

opengl

framebuffer

sdl-2