使用 glBlitFramebuffer 显示纹理
Using glBlitFramebuffer to display a texture
我正在尝试实现一个简单的多通道渲染方案。我首先将场景的多重采样版本 blit 到 FBO beforeEffectsContext.fbo
。如果我然后将其 blit 到应用程序提供的 FB 它工作正常。但我想在场景上再做一次模糊处理。因此,我将 COLOR_ATTACHMENT0
中的纹理绑定到 beforeEffectsContext.fbo
中,对其进行采样,绘制一个带有模糊效果的四边形添加到另一个帧缓冲区 blurContext.fbo
.
如果我知道使用与四边形和纹理采样相同的方法将 blurContext.fbo
的颜色附件的内容显示到屏幕上,它就可以工作并且我得到一个模糊的场景。
但是如果我在这一步尝试使用 glBlitFramebuffer()
,我会得到一个黑屏。问题似乎出在我对blitting过程和FBO的理解上。
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);
在为绘图绑定默认帧缓冲区 (0) 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。
我正在尝试实现一个简单的多通道渲染方案。我首先将场景的多重采样版本 blit 到 FBO beforeEffectsContext.fbo
。如果我然后将其 blit 到应用程序提供的 FB 它工作正常。但我想在场景上再做一次模糊处理。因此,我将 COLOR_ATTACHMENT0
中的纹理绑定到 beforeEffectsContext.fbo
中,对其进行采样,绘制一个带有模糊效果的四边形添加到另一个帧缓冲区 blurContext.fbo
.
如果我知道使用与四边形和纹理采样相同的方法将 blurContext.fbo
的颜色附件的内容显示到屏幕上,它就可以工作并且我得到一个模糊的场景。
但是如果我在这一步尝试使用 glBlitFramebuffer()
,我会得到一个黑屏。问题似乎出在我对blitting过程和FBO的理解上。
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);
在为绘图绑定默认帧缓冲区 (0) 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。