ios - 在纹理中转换 UIImage

Question

在我的 opengl 项目中，我需要将 UIImage 转换为纹理；有什么办法呢？你能帮助我吗？

Answer 1

我没有测试以下内容，但我将分 3 个步骤分解转换：

1. 为您的图像提取信息：

   UIImage* image = [UIImage imageNamed:@"imageToApplyAsATexture.png"];
   CGImageRef imageRef = [image CGImage];
   int width = CGImageGetWidth(imageRef);
   int height = CGImageGetHeight(imageRef);
   

2. 分配textureData具有上述属性的 a：

   GLubyte* textureData = (GLubyte *)malloc(width * height * 4); // if 4 components per pixel (RGBA)
   
   CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
   NSUInteger bytesPerPixel = 4;
   NSUInteger bytesPerRow = bytesPerPixel * width;
   NSUInteger bitsPerComponent = 8;  
   CGContextRef context = CGBitmapContextCreate(textureData, width, height,
                                                bitsPerComponent, bytesPerRow, colorSpace,
                                                kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
   
   CGColorSpaceRelease(colorSpace);
   
   CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
   CGContextRelease(context);
   

3. 设置你的纹理：

   GLuint textureID;    
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
   glGenTextures(1, &textureID);
   
   glBindTexture(GL_TEXTURE_2D, textureID);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);
   

编辑：

阅读此书；从一张图像到纹理的转换以及在 iOS 环境中应用纹理，一切都得到了解释。

Answer 2

这是从 UIImage 中获取纹理的快速版本

func setupTexture(sourceImage: UIImage) -> GLuint {

guard let textureImage = sourceImage.cgImage else {
    print("Failed to load image")
    return 0
}

let width = textureImage.width
let height = textureImage.height

/*
 it will write one byte each for red, green, blue, and alpha – so 4 bytes in total.
 */

let textureData = calloc(width * height * 4, MemoryLayout<GLubyte>.size) //4 components per pixel (RGBA)
let spriteContext = CGContext(data: textureData,
                              width: width,
                              height: height,
                              bitsPerComponent: 8,
                              bytesPerRow: width * 4,
                              space: textureImage.colorSpace!,
                              bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)

spriteContext?.draw(textureImage, in: CGRect(x: 0, y: 0, width: width, height: height))

var textName = GLuint()
glGenTextures(1, &textName)
glBindTexture(GLenum(GL_TEXTURE_2D), textName)
glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_MIN_FILTER), GL_NEAREST)
glTexImage2D(GLenum(GL_TEXTURE_2D), 0, GL_RGBA, GLsizei(width),
             GLsizei(height), 0, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), textureData)

return textName

}

注意：需要记住，Core Graphics 在加载图像时会翻转图像。

Answer 3

使用 GLKit 框架的另一种方法：

//Path to image
NSString *path = [[NSBundle mainBundle] pathForResource:@"textureImage" ofType:@"png"];

//Set eaglContext
[EAGLContext setCurrentContext:[[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]];

//Create texture
NSError *theError;    
GLKTextureInfo *texture = [GLKTextureLoader textureWithContentsOfFile:filePath options:nil error:&theError];
glBindTexture(texture.target, texture.name);

texture.name是纹理的 OpenGL 上下文名称。