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命令工作正常： -

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);

但当我使用深度缓冲和色彩缓冲进行多重采样glreadpixels（）时不捕获任何像素数据与早期代码....对于多次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);

任何想法如何使用多采样技术捕获正确的像素数据....或者我在做什么有问题？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

使用多重采样FBO时，您不能只读取样本缓冲区（因为它不包含简单像素） ）。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来实现此目的（让我们称之为 resultFramebuffer ）你需要阅读然后调用的必要的renderbuffer存储：

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读取（当然实际的常量和函数名称可能包含OES或苹果）。如果您不需要最终深度值，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.

编辑：正如您所写的那样您的评论和我搜索的内容，有一个专用函数 glResolveMultisampleFramebufferAPPLE 您必须使用而不是 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.

这篇关于使用带有多重采样的glReadPixel（）读取数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！