作者：字节流动
来源：https://blog.csdn.net/Kennethdroid/article/details/109032497
OpenGL ES 帧缓冲区位块传送
帧缓冲区位块传送（Blit）也是 OpenGL ES 3.0 的新特性，主要用于帧缓冲区之间的像素拷贝，性能高且使用方便，可以指定缓冲区任意矩形区域的像素拷贝。
本文的绘制流程是，新建一个 FBO 绑定纹理作为颜色附着，然后绑定该帧缓冲区进行一次离屏渲染，最后绑定渲染到屏幕的缓冲区作为渲染缓冲区，从新的帧缓冲区中拷贝像素。
渲染代码：
//首先获取当前默认帧缓冲区的 id GLint defaultFrameBuffer = GL_NONE; glGetIntegerv(GL_FRAMEBUFFER_BINDING, &defaultFrameBuffer); //绑定我们新创建的帧缓冲区进行渲染 glBindFramebuffer(GL_FRAMEBUFFER, m_FBO); glViewport ( 0, 0, m_RenderImage.width, m_RenderImage.height); glClear(GL_COLOR_BUFFER_BIT); glDrawBuffers(ATTACHMENT_NUM, attachments); glUseProgram (m_ProgramObj); glBindVertexArray(m_VaoId); UpdateMVPMatrix(m_MVPMatrix, 0, m_AngleY, (float)screenW / screenH); glUniformMatrix4fv(m_MVPMatLoc, 1, GL_FALSE, &m_MVPMatrix[0][0]); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, m_TextureId); glUniform1i(m_SamplerLoc, 0); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, (const void *)0); //绑定默认的帧缓冲区对象，将像素从新建的帧缓冲区拷贝到当前默认的帧缓冲区 glBindFramebuffer(GL_DRAW_FRAMEBUFFER, defaultFrameBuffer); glViewport ( 0, 0, m_SurfaceWidth, m_SurfaceHeight); glClear(GL_COLOR_BUFFER_BIT); //位块传送 BlitTextures();
进行帧缓冲区间位块传之前，需要指定好源帧缓冲区 GL_READ_FRAMEBUFFER 和目标帧缓冲区 GL_DRAW_FRAMEBUFFER，下面代码实现是将四个颜色附着对应的缓冲区像素，分别拷贝到当前渲染缓冲区中的 1/4 矩形区域内：
void FBOBlitSample::BlitTextures() { //很重要，指定源帧缓冲区 glBindFramebuffer(GL_READ_FRAMEBUFFER, m_FBO); glReadBuffer(GL_COLOR_ATTACHMENT0); glBlitFramebuffer(0, 0, m_RenderImage.width, m_RenderImage.height, 0, 0, m_SurfaceWidth/2, m_SurfaceHeight/2, GL_COLOR_BUFFER_BIT, GL_LINEAR); glReadBuffer(GL_COLOR_ATTACHMENT1); glBlitFramebuffer(0, 0, m_RenderImage.width, m_RenderImage.height, m_SurfaceWidth/2, 0, m_SurfaceWidth, m_SurfaceHeight/2, GL_COLOR_BUFFER_BIT, GL_LINEAR); glReadBuffer(GL_COLOR_ATTACHMENT2); glBlitFramebuffer(0, 0, m_RenderImage.width, m_RenderImage.height, 0, m_SurfaceHeight/2, m_SurfaceWidth/2, m_SurfaceHeight, GL_COLOR_BUFFER_BIT, GL_LINEAR); glReadBuffer(GL_COLOR_ATTACHMENT3); glBlitFramebuffer(0, 0, m_RenderImage.width, m_RenderImage.height, m_SurfaceWidth/2, m_SurfaceHeight/2, m_SurfaceWidth, m_SurfaceHeight, GL_COLOR_BUFFER_BIT, GL_LINEAR); }
最后呈现的效果是将四张图像渲染到一个屏幕上。
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