将OpenGL ES 2.0渲染为图像

Question

我正在尝试对图像文件进行一些OpenGL ES 2.0渲染，而不依赖于屏幕上向用户显示的渲染。我要呈现的图像与用户的屏幕大小不同。我只需要一个GL_RGB数据的字节数组。我熟悉glReadPixels，但我不认为它会在这种情况下做到这一点，因为我没有从已经渲染的用户屏幕拉出。

伪代码：

// Switch rendering to another buffer (framebuffer? renderbuffer?) 

// Draw code here 

// Save byte array of rendered data GL_RGB to file 

// Switch rendering back to user's screen. 

我怎么能做到这一点，而无需中断用户的显示？我宁愿不必闪烁用户的屏幕，为单个帧绘制我想要的信息，glReadPixel-ing，然后让它消失。

同样，我不希望它向用户显示任何内容。这是我的代码。不工作..我错过了什么吗？

unsigned int canvasFrameBuffer; 
bglGenFramebuffers(1, &canvasFrameBuffer); 
bglBindFramebuffer(BGL_RENDERBUFFER, canvasFrameBuffer); 
unsigned int canvasRenderBuffer; 
bglGenRenderbuffers(1, &canvasRenderBuffer); 
bglBindRenderbuffer(BGL_RENDERBUFFER, canvasRenderBuffer); 
bglRenderbufferStorage(BGL_RENDERBUFFER, BGL_RGBA4, width, height); 
bglFramebufferRenderbuffer(BGL_FRAMEBUFFER, BGL_COLOR_ATTACHMENT0, BGL_RENDERBUFFER, canvasRenderBuffer); 

unsigned int canvasTexture; 
bglGenTextures(1, &canvasTexture); 
bglBindTexture(BGL_TEXTURE_2D, canvasTexture); 
bglTexImage2D(BGL_TEXTURE_2D, 0, BGL_RGB, width, height, 0, BGL_RGB, BGL_UNSIGNED_BYTE, 0); 
bglFramebufferTexture2D(BGL_FRAMEBUFFER, BGL_COLOR_ATTACHMENT0, BGL_TEXTURE_2D, canvasTexture, 0); 

Matrix::matrix_t identity; 
Matrix::LoadIdentity(&identity); 
bglClearColor(1.0f, 1.0f, 1.0f, 1.0f); 
bglClear(BGL_COLOR_BUFFER_BIT); 
Draw(&identity, &identity, this); 
bglFlush(); 
bglFinish(); 

byte *buffer = (byte*)Z_Malloc(width * height * 4, ZT_STATIC); 
bglReadPixels(0, 0, width, height, BGL_RGB, BGL_UNSIGNED_BYTE, buffer); 
SaveTGA("canvas.tga", buffer, width, height); 
Z_Free(buffer); 

// unbind frame buffer 
bglBindRenderbuffer(BGL_RENDERBUFFER, 0); 
bglBindFramebuffer(BGL_FRAMEBUFFER, 0); 
bglDeleteTextures(1, &canvasTexture); 
bglDeleteRenderbuffers(1, &canvasRenderBuffer); 
bglDeleteFramebuffers(1, &canvasFrameBuffer); 

Answer 1

这里的解决方案，任何人谁需要它：

// Create framebuffer 
unsigned int canvasFrameBuffer; 
glGenFramebuffers(1, &canvasFrameBuffer); 
glBindFramebuffer(GL_RENDERBUFFER, canvasFrameBuffer); 

// Attach renderbuffer 
unsigned int canvasRenderBuffer; 
glGenRenderbuffers(1, &canvasRenderBuffer); 
glBindRenderbuffer(GL_RENDERBUFFER, canvasRenderBuffer); 
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA4, width, height); 
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, canvasRenderBuffer); 

    // Clear the target (optional) 
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); 
glClear(GL_COLOR_BUFFER_BIT); 

    // Draw whatever you want here 

char *buffer = (char*)malloc(width * height * 3); 
glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, buffer); 
SaveTGA("canvas.tga", buffer, width, height); // Your own function to save the image data to a file (in this case, a TGA) 
free(buffer); 

// unbind frame buffer 
glBindRenderbuffer(GL_RENDERBUFFER, 0); 
glBindFramebuffer(GL_FRAMEBUFFER, 0); 
glDeleteRenderbuffers(1, &canvasRenderBuffer); 
glDeleteFramebuffers(1, &canvasFrameBuffer); 

Answer 2

您可以渲染到纹理，读取像素并绘制具有该纹理的四边形（如果要显示给用户）。它不应该闪烁，但它会明显降低性能。

在iOS设备上，例如：

• OpenGL ES Render to Texture
• Reading a openGL ES texture to a raw array