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POOpenGL ES (IPhone) alpha blending looks weird
 

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  1. POOpenGL ES (IPhone) alpha blending looks weird
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    <p>I'm writing a game for IPhone in Opengl ES, and I'm experiencing a problem with alpha blending:</p> <p>I'm using <code>glBlendFunc(Gl.GL_SRC_ALPHA, Gl.GL_ONE_MINUS_SRC_ALPHA)</code> to achieve alpha blending and trying to compose a scene with several "layers" so I can move them separately instead of having a static image. I created a preview in photoshop and then tried to achieve the same result in the iphone, but a black halo is shown when I blend a texture with semi-transparent regions.</p> <p>I attached an image. In the left is the screenshot from the iphone, and in the right is what it looks like when I make the composition in photoshop. The image is composed by a gradient and a sand image with feathered edges.</p> <p>Is this the expected behaviour? Is there any way I can avoid the dark borders?</p> <p>Thanks.</p> <p><strong>EDIT</strong>: I'm uploading the portion of the png containing the sand. The complete png is 512x512 and has other images too.</p> <p>I'm loading the image using the following code:</p> <pre><code>NSString *path = [NSString stringWithUTF8String:filePath]; NSData *texData = [[NSData alloc] initWithContentsOfFile:path]; UIImage *image = [[UIImage alloc] initWithData:texData]; if (image == nil) NSLog(@"ERROR LOADING TEXTURE IMAGE"); GLuint width = CGImageGetWidth(image.CGImage); GLuint height = CGImageGetHeight(image.CGImage); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); void *imageData = malloc( height * width * 4 ); CGContextRef context = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big ); CGColorSpaceRelease( colorSpace ); CGContextClearRect( context, CGRectMake( 0, 0, width, height ) ); CGContextTranslateCTM( context, 0, height - height ); CGContextDrawImage( context, CGRectMake( 0, 0, width, height ), image.CGImage ); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData); CGContextRelease(context); free(imageData); [image release]; [texData release]; </code></pre> <hr> <p><img src="https://i.stack.imgur.com/bPGwB.png" alt="alt text"> <img src="https://i.stack.imgur.com/Ig0GR.png" alt="alt text"></p>
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