opengl - 使用 glBlitFramebuffer 显示纹理

Question

我正在尝试实现一个简单的多 channel 渲染方案。我首先将场景的多重采样版本传输到 FBO beforeEffectsContext.fbo 。如果我然后将其传输到应用程序提供的 FB，它就可以正常工作。但我想对场景进行另一遍以模糊它。因此，我将纹理绑定(bind)在 COLOR_ATTACHMENT0 中在 beforeEffectsContext.fbo ，对其进行采样，绘制一个四边形，并将模糊效果添加到另一个帧缓冲区 blurContext.fbo .

如果我知道显示blurContext.fbo的内容使用与四边形和纹理采样相同的方法将颜色附加到屏幕上，它起作用了，我得到了一个模糊的场景。

但是如果我尝试使用glBlitFramebuffer()相反，在这一步中，我看到黑屏。问题似乎在于我对位 block 传输过程和 FBO 的误解。

blurContext.fbo的初始化代码:

// BeforeEffects Framebuffer
glGenFramebuffers(1, &renderContext->beforeEffectsContext.fbo);
glBindFramebuffer(GL_FRAMEBUFFER, renderContext->beforeEffectsContext.fbo);

glGenTextures(1, &renderContext->beforeEffectsContext.colorAttachment);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, renderContext->beforeEffectsContext.colorAttachment);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 800, 600, 0, GL_RGBA, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderContext->beforeEffectsContext.colorAttachment, 0);

// Blur Framebuffer
glGenFramebuffers(1, &renderContext->blurContext.fbo);
glBindFramebuffer(GL_FRAMEBUFFER, renderContext->blurContext.fbo);

glGenTextures(1, &renderContext->blurContext.colorAttachment);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, renderContext->blurContext.colorAttachment);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 800, 600, 0, GL_RGBA, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderContext->blurContext.colorAttachment, 0);

渲染:

// Draw to the MSampled scene to the BeforeEffects framebuffer
glBindFramebuffer(GL_READ_FRAMEBUFFER, renderContext->multiSamplingContext.fbo);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, renderContext->beforeEffectsContext.fbo);
glBlitFramebuffer(0, 0, 800, 600, 0, 0, 800, 600, GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT, GL_NEAREST);

// Sample the texture attached to the beforeEffects FBO and draw to the blur FBO
glBindTexture(GL_TEXTURE_2D, renderContext->beforeEffectsContext.colorAttachment);
glBindFramebuffer(GL_FRAMEBUFFER, renderContext->blurContext.fbo);
glViewport(0, 0, 800, 600);

glUseProgram(renderContext->blurProgramContext.program);
glBindVertexArray(renderContext->vaoBlur);

glDrawArrays(GL_QUADS, 0, 4);

glUseProgram(0);
glBindVertexArray(0);

// Blit the content of the blur FBO to the app-provided Framebuffer (doesn't work, black screen)
glBindFramebuffer(GL_READ_FRAMEBUFFER, renderContext->blurContext.fbo);
glReadBuffer(GL_COLOR_ATTACHMENT0);
glBindFramebuffer(GL_DRAW_BUFFER, 0);
glViewport(0, 0, 800, 600);
glBlitFramebuffer(0, 0, 800, 600, 0, 0, 800, 600, GL_COLOR_BUFFER_BIT,
    GL_NEAREST);

Answer 1

在绑定(bind)默认帧缓冲区 (0) 进行绘制的行中，目标为 GL_DRAW_BUFFER。根据https://www.opengl.org/sdk/docs/man/html/glBindFramebuffer.xhtml设置绘制帧缓冲区的正确枚举是 GL_DRAW_FRAMEBUFFER。如果添加对 glGetError 的调用，您可能会看到 GL_INVALID_ENUM 错误。