ios - 将多个EAGLView转换为UIImage

我在每个单元格内都有3个UITableView的EAGLView，用户可以在其中绘制一些内容(在Apple GLPaint之后，我只是使用该示例中的PaintingView类)

我正在尝试在按钮按下事件时将此3 EAGLView转换为3个不同的UIImage，但生成的UIImage始终等于最后编辑的EAGLView
这是我正在使用的代码(从here复制):

- (UIImage*)saveImageFromGLView:(UIView *)glView withName:(NSString *)name{

if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES)
{
    /// This IS being activated with code 0
    NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES));
}

int s = 1;
UIScreen* screen = [ UIScreen mainScreen ];
if ( [ screen respondsToSelector:@selector(scale) ] )
    s = (int) [ screen scale ];

const int w = self.frame.size.width;
const int h = self.frame.size.height;
const NSInteger myDataLength = w * h * 4 * s * s;
// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, w*s, h*s, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
// gl renders "upside down" so swap top to bottom into new array.
// there's gotta be a better way, but this works.
GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
for(int y = 0; y < h*s; y++)
{
    memcpy( buffer2 + (h*s - 1 - y) * w * 4 * s, buffer + (y * 4 * w * s), w * 4 * s );
}
free(buffer); // work with the flipped buffer, so get rid of the original one.

// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * w * s;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef imageRef = CGImageCreate(w*s, h*s, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// then make the uiimage from that
UIImage *myImage = [ UIImage imageWithCGImage:imageRef scale:s orientation:UIImageOrientationUp ];

// Create path.
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:name];

// Save image.
[UIImagePNGRepresentation(myImage) writeToFile:filePath atomically:YES];

CGImageRelease( imageRef );
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpaceRef);
free(buffer2);

return myImage;
}

我认为这是一个上下文问题，如何获得三个不同的图像？

最佳答案

假设您对这些视图使用using retained backing(否则在显示到屏幕后glReadPixels()不起作用)，我的猜测是每个视图都有不同的OpenGL ES上下文。 glReadPixels()将仅从当前 Activity 的上下文中拉出，从而从最后呈现的视图中拉出。

在上面的方法中从每个视图的上下文读取之前，您将需要使用如下代码:

[EAGLContext setCurrentContext:context];

从OpenGL ES渲染UIView提取上下文的位置。您可能需要将该上下文设置为UIView子类的只读属性，然后更改上述方法以将该子类纳入其中。然后，您可以在使用glReadPixels()之前切换到适当的上下文。

作为附带问题，您不应在上面使用glCheckFramebufferStatusOES()。那只真正属于您的帧缓冲区创建代码，而在上述方法中并没有真正的目的。