使用带有多重采样的 glReadPixel() 读取数据 [英] Reading data using glReadPixel() with multisampling

问题描述

目前我正在尝试从帧缓冲区读取像素数据，以便在 IOS 中捕获屏幕.使用以下代码设置帧缓冲区时，GlreadPixels 命令可以正常工作:-

Presently I am trying to read the pixel data from the frame Buffer in order to capture the screen in IOS. GlreadPixels command works fine when using the following code to setup frame buffer :-

//buffers
// Create a depth buffer that has the same size as the color buffer.
glGenRenderbuffersOES(1, &m_depthRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, m_depthRenderbuffer);
glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT24_OES, width, height);

// Create the framebuffer object.

glGenFramebuffersOES(1, &framebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES,
                             GL_RENDERBUFFER_OES, m_colorRenderbuffer);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES,
                             GL_RENDERBUFFER_OES, m_depthRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, m_colorRenderbuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);

但是当我使用深度缓冲区和颜色缓冲区进行多重采样时，glreadpixels() 不会像之前的代码那样捕获任何像素数据....对于多重采样，我使用以下代码:-

but when I use depth buffer and colorbuffer for Multi-Sampling glreadpixels() don't capture any pixel data as with earlier code ....for multi-sampling I use following code :-

glGenFramebuffersOES(1, &sampleFramebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, sampleFramebuffer);

//GLuint sampleColorRenderbuffer;
glGenRenderbuffersOES(1, &sampleColorRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, sampleColorRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_RGBA8_OES, width, height);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, sampleColorRenderbuffer);

//glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_RGBA8_OES, width, height);
//glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, sampleColorRenderbuffer);

GLuint sampleDepthRenderbuffer;
glGenRenderbuffersOES(1, &sampleDepthRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, sampleDepthRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_DEPTH_COMPONENT24_OES, width, height);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, sampleDepthRenderbuffer);
//glBindRenderbufferOES(GL_RENDERBUFFER_OES,sampleColorRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, m_colorRenderbuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, sampleFramebuffer);

我使用以下代码读取像素数据:-

I use the follwing code to read pixel data :-

CGRect screenBounds = [[UIScreen mainScreen] bounds];

int backingWidth = screenBounds.size.width;
int backingHeight =screenBounds.size.height;

glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
NSInteger myDataLength = backingWidth * backingHeight * 4;

buffer= (GLuint *) malloc(myDataLength);
glReadPixels(0, 0, backingWidth, backingHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

知道如何使用多重采样技术捕获正确的像素数据......还是我做错了什么?请指导我正确的方向.谢谢

Any idea how to capture correct pixel data with multi-Sampling technique....or Am I doing something wrong? Please guide me in right direction. Thanks

推荐答案

当使用多采样 FBO 时，您不能只读取采样缓冲区(因为它不包含简单的像素).您首先需要将样本缓冲区解析为单个缓冲区.

When using multisampled FBOs you cannot just read the sample buffer (as it doesn't contain simple pixels). You first need to resolve the sample buffers into a single buffer.

您可以通过创建另一个非多重采样 FBO(我们称其为 resultFramebuffer)和您想要读取的必要渲染缓冲区存储然后调用:

You do this by creating another non-multisampled FBO (let's call it resultFramebuffer) with the neccessary renderbuffer storage you want to read and then calling:

glBindFramebuffer(GL_READ_FRAMEBUFFER, sampleFramebuffer);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, resultFramebuffer);
glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT, GL_NEAREST);

然后你从结果缓冲区中读取(当然实际的常量和函数名可能包含 OES 或 APPLE).如果您不需要最终的深度值，则结果缓冲区不需要深度渲染缓冲区.

And then you read from the result buffer (of course the actual constant and function names may contain OES or APPLE). If you don't need the final depth values, the result buffer doesn't need a depth renderbuffer.

正如您在评论中所写以及我搜索的内容，您必须使用一个专用函数 glResolveMultisampleFramebufferAPPLE 代替 glBlitFramebuffer.其余的保持不变.

As you wrote in your comment and what I searched, there is a dedicated function glResolveMultisampleFramebufferAPPLE you have to use instead of glBlitFramebuffer. The rest stays the same.

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