旋转矩阵

让图形的顶点旋转180度，纹理保持不变。

GLuint rotate = glGetUniformLocation(self.myPrograme, "rotateMatrix");
float radians = 180 * 3.14159f / 180.0f;
float s = sin(radians);
float c = cos(radians);
    
GLfloat zRotation[16] = {
    c, -s, 0, 0,
    s, c, 0, 0,
    0, 0, 1.0, 0,
    0.0, 0, 0, 1.0
};
glUniformMatrix4fv(rotate, 1, GL_FALSE, (GLfloat *)&zRotation[0]);

GSL代码

attribute vec4 position;
attribute vec2 textCoordinate;
uniform mat4 rotateMatrix;

varying lowp vec2 varyTextCoord;

void main()
{
    varyTextCoord = textCoordinate;
  
    vec4 vPos = position;
    vPos = vPos * rotateMatrix;
    gl_Position = vPos;
}

旋转解压时的图片

CGImageRef spriteImage = [UIImage imageNamed:fileName].CGImage;

size_t width = CGImageGetWidth(spriteImage);
size_t height = CGImageGetHeight(spriteImage);
GLubyte * spriteData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));

CGContextRef spriteContext = CGBitmapContextCreate(spriteData, width, height, 8, width*4,CGImageGetColorSpace(spriteImage), kCGImageAlphaPremultipliedLast);
  
CGRect rect = CGRectMake(0, 0, width, height);
CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), spriteImage);

CGContextTranslateCTM(spriteContext, rect.origin.x, rect.origin.y);
CGContextTranslateCTM(spriteContext, 0, rect.size.height);
CGContextScaleCTM(spriteContext, 1.0, -1.0);
CGContextTranslateCTM(spriteContext, -rect.origin.x, -rect.origin.y);
CGContextDrawImage(spriteContext, rect, spriteImage); 

CGContextRelease(spriteContext);
glBindTexture(GL_TEXTURE_2D, 0);

CGContextTranslateCTM(spriteContext, rect.origin.x, rect.origin.y);
平移画布

-w512
CGContextTranslateCTM(spriteContext, 0, rect.size.height);
将画布平移到某个位置

-w500
CGContextScaleCTM(spriteContext, 1.0, -1.0);
翻转画布

-w520
CGContextTranslateCTM(spriteContext, -rect.origin.x, -rect.origin.y);
将画布移动到原来的位置

-w499

修改片元着色器

varying lowp vec2 varyTextCoord;
uniform sampler2D colorMap;
void main()
{
    gl_FragColor = texture2D(colorMap, vec2(varyTextCoord.x,1.0-varyTextCoord.y));
}

修改顶点着色器

attribute vec4 position;
attribute vec2 textCoordinate;
varying lowp vec2 varyTextCoord;

void main()
{
    varyTextCoord = vec2(textCoordinate.x,1.0-textCoordinate.y);
    gl_Position = position;
}

修改源纹理坐标

 GLfloat attrArr[] =
 {
 0.5f, -0.5f, 0.0f,        1.0f, 1.0f, //右下
 -0.5f, 0.5f, 0.0f,        0.0f, 0.0f, // 左上
 -0.5f, -0.5f, 0.0f,       0.0f, 1.0f, // 左下
 0.5f, 0.5f, 0.0f,         1.0f, 0.0f, // 右上
 -0.5f, 0.5f, 0.0f,        0.0f, 0.0f, // 左上
 0.5f, -0.5f, 0.0f,        1.0f, 1.0f, // 右下
 };
 */