使用深度缓冲区和抗锯齿技术时，通过glreadpixel()读取数据时出现问题 [英] Problem reading data by glreadpixel() while using depth buffer and anti-aliasing technique

问题描述

我想使用glreadpixel()捕获游戏的屏幕. 它在ios版本3.1.1的2g iphone上也可以在模拟器上正常工作. 但在ios版本4.2.1的ipad上却没有.我开始知道与此有关的问题.适用于特定设备(ipad)上的ios 4.0以上版本 我们绑定深度缓冲区并使用抗锯齿技术.当我们使用opengl的glreadpixel()从帧缓冲区捕获数据时，将在目标缓冲区中返回全0 ...

I want to capture the screen of my game using glreadpixel(). it works fine over simulator also on 2g iphone with ios version 3.1.1 . but on ipad with ios version 4.2.1 it doesnt . i came to know the issue regarding this. for ios version 4.0 above on a particular device (ipad) we bind depth buffer and use anti-aliasing technique. And when we use glreadpixel() of opengl that capture data from frame buffer returns all 0 in the destination buffer...

如果我们不将深度缓冲区绑定到帧缓冲区，并且不使用抗锯齿技术，则效果很好.

if we dont bind the depth buffer to frame buffer and dont use the anti-aliasing technique it works fine.

我使用的代码是:-

CGRect screenBounds = [[UIScreen mainScreen]边界];

CGRect screenBounds = [[UIScreen mainScreen] bounds];

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

NSLog(@"width : %f Height : %f",screenBounds.size.width,screenBounds.size.height);
CGSize esize = CGSizeMake(screenBounds.size.width, screenBounds.size.height);
NSInteger myDataLength = esize.width * esize.height * 4;
GLuint *buffer = (GLuint *) malloc(myDataLength);
glReadPixels(0, 0, esize.width, esize.height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
for(int y = 0; y < backingHeight / 2; y++) {
    for(int xt = 0; xt < backingWidth; xt++) {
        GLuint top = buffer[y * backingWidth + xt];
        GLuint bottom = buffer[(backingHeight - 1 - y) * backingWidth + xt];
        buffer[(backingHeight - 1 - y) * backingWidth + xt] = top;
        buffer[y * backingWidth + xt] = bottom;
    }
}
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, myDataLength, releaseScreenshotData);
const int bitsPerComponent = 8;
const int bitsPerPixel = 4 * bitsPerComponent;
const int bytesPerRow = 4 * backingWidth;

CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGImageRef imageRef = CGImageCreate(backingWidth,backingHeight, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
/*
UIImage *myImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
[snap setImage:myImage];
[self addSubview:snap];*/

有什么想法在opegl es中使用glreadpixel()或任何其他类似函数时如何在深度锯齿中包含深度信息?

Any idea how to include depth information with anti-aliasing while using glreadpixel() or any other similar function in opegl es ?

推荐答案

想通了！您必须在调用glReadPixels()之前将resolve-framebuffer绑定回GL_FRAMEBUFFER

Figured it out! You have to bind the resolve-framebuffer back to GL_FRAMEBUFFER before calling glReadPixels()

glBindFramebuffer(GL_FRAMEBUFFER, resolveFramebuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
glReadPixels(xpos, ypos, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, pixelByteArray);
glBindFramebuffer(GL_FRAMEBUFFER, sampleFrameBuffer);

在渲染下一帧之前，请确保将样本帧缓冲区绑定为GL_FRAMEBUFFER，但是默认的Apple模板已经做到了这一点.

Make sure to bind your sample-framebuffer as GL_FRAMEBUFFER before rendering the next frame, but the default Apple template already does this.

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