将 OpenGL ES 2.0 渲染到图像

Question

我正在尝试对图像文件进行一些 OpenGL ES 2.0 渲染，与屏幕上显示给用户的渲染无关。我正在渲染的图像与用户屏幕的大小不同。我只需要一个 GL_RGB 数据的字节数组。我熟悉 glReadPixels，但我认为在这种情况下它不会起作用，因为我没有从已经渲染的用户屏幕中提取。

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.

如何在不中断用户显示的情况下执行此操作？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。不起作用..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

以下是解决方案，适合任何需要的人：

    // 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，读取像素并使用该纹理绘制一个四边形（如果您想向用户展示）。它不应该闪烁，但会明显降低性能。

以 iOS 为例：

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