ios - 使用 glReadPixel() 和多重采样读取数据

Question

目前我正在尝试从帧缓冲区中读取像素数据，以便在 IOS 中捕获屏幕。当使用以下代码设置帧缓冲区时，GlreadPixels 命令工作正常:-

//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:-

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:-

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......或者我做错了什么？请指导我正确的方向。谢谢

Answer 1

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)。您首先需要将样本缓冲区解析为单个缓冲区。

为此，您可以创建另一个非多重采样 FBO(我们称它为 resultFramebuffer)，其中包含您要读取的必要渲染缓冲区存储，然后调用:

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称可能包含 OES 或 APPLE)。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。

编辑:正如您在评论和我搜索的内容中所写，您必须使用一个专用函数 glResolveMultisampleFramebufferAPPLE 而不是 glBlitFramebuffer .其余保持不变。