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我正在使用 OpenGL ES 2.0 编写一个 iOS 视频应用程序来进行图像处理。

我的视频输入和输出格式是 YUV 4:2:0，这是 iPhone 3GS 之后大多数设备的原生像素格式。对于 A5 及更高的处理器，我只需创建一个亮度纹理和一个色度纹理，然后将它们附加到屏幕外帧缓冲区。我创建我的纹理如下：

CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault,
                                                   _videoTextureCache,
                                                   pixelBuffer,
                                                   NULL,
                                                   GL_TEXTURE_2D,
                                                   GL_RED_EXT,
                                                   (int)CVPixelBufferGetWidthOfPlane(pixelBuffer, 0),
                                                   (int)CVPixelBufferGetHeightOfPlane(pixelBuffer, 0),
                                                   GL_RED_EXT,
                                                   GL_UNSIGNED_BYTE,
                                                   0,
                                                   &lumaTexture);

然后我将它附加到程序中，例如：

glActiveTexture([self getTextureUnit:textureUnit]);
glBindTexture(CVOpenGLESTextureGetTarget(texture), CVOpenGLESTextureGetName(texture));
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
if(uniform != -1)
{
    glUniform1i(uniforms[uniform], textureUnit);
}

在我的着色器中，我可以简单地做：

gl_FragColor.r = texture2D(SamplerY, textureRead).r;

将亮度值分配给缓冲区并将生成的视频帧保存到磁盘。

不幸的是，我遇到了 iPhone 4 的问题，因为它没有使用 A5 处理器，因此GL_RED_EXT不受支持。

I have then tried to figure out a way to write to a 1 channel luma buffer in OpenGL ES, but keep running into problems. I tried simply changing the GL_RED_EXT to GL_LUMINANCE but found out that it isn't possible to write to GL_LUMINANCE.

I then tried registering a color attachment and a depth attachment as:

GLuint colorRenderbuffer;
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGB8_OES, (int)CVPixelBufferGetWidthOfPlane(renderData.destinationPixelBuffer, 0), (int)CVPixelBufferGetHeightOfPlane(renderData.destinationPixelBuffer, 0));
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                              GL_RENDERBUFFER, colorRenderbuffer);

GLuint depthRenderbuffer;
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, (int)CVPixelBufferGetWidthOfPlane(renderData.destinationPixelBuffer, 0), (int)CVPixelBufferGetHeightOfPlane(renderData.destinationPixelBuffer, 0));
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
                              GL_RENDERBUFFER, depthRenderbuffer);

Writing to the depth buffer in my fragment shader:

gl_FragDepth.z = texture2D(SamplerY, textureRead).r;

And then writing the result to the pixel buffer as:

glReadPixels(0, 0, (int)CVPixelBufferGetWidthOfPlane(renderData.destinationPixelBuffer, 0), (int)CVPixelBufferGetHeightOfPlane(renderData.destinationPixelBuffer, 0), GL_LUMINANCE, GL_UNSIGNED_BYTE, CVPixelBufferGetBaseAddressOfPlane(renderData.destinationPixelBuffer, 0));

But again I read in the specs that OpenGL ES 2.0 does not support writing directly to the depth buffer.

So I am left with no obvious way to create a single channel color attachment and I am not sure how I could write to a RGB color attachment and only copy one channel to my pixel buffer.

Sorry for the long post, just wanted to give as much information as possible.

Any ideas?

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1 回答 1

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So how I ended up solving this was to use GL_LUMINANCE and GL_LUMINANCE_ALPHA instead of RED and RG if the extensions aren't available. I would then add a step after my render passes to use glReadPixels to manually copy the pixels into the expected format of my preallocated pixelbuffers.

于 2016-02-15T19:25:49.907 回答