#import "ViewController.h"
#import <GLKit/GLKit.h>

//vertex struct type
typedef struct {
    GLKVector3 positionCoord; // (x,y,z)
    GLKMatrix2 textureCoord; // (u, v)
    
} SenceVertex;


@interface ViewController ()

@property (nonatomic, assign) SenceVertex *vertices; //顶点数组
@property (nonatomic, strong) EAGLContext *context;

@end

@implementation ViewController

#pragma mark -
#pragma mark - override methods
- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    [self commonInit];
}

#pragma mark -
#pragma mark - private methods
- (void)commonInit {
    //create the context, using version 2.0
    self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
    [EAGLContext setCurrentContext:self.context];
    
    //create the vertex array
    self.vertices = malloc(sizeof(SenceVertex) * 4); //4个顶点
    
    self.vertices[0] = (SenceVertex){{-1, 1, 0},{ 0, 1 }}; //左上角
    self.vertices[1] = (SenceVertex){{-1, -1, 0},{0 ,0}}; //左下角
    self.vertices[2] = (SenceVertex){{1, 1, 0},{1, 1}}; //右上角
    self.vertices[3] = (SenceVertex){{1, -1, 0},{1, 0}}; //右下角
    
    //create a layer for displaying the texture
    
    CAEAGLLayer *layer = [CAEAGLLayer layer];
    layer.frame = CGRectMake(0, 100, self.view.frame.size.width, self.view.frame.size.width);
    layer.contentsScale = [[UIScreen mainScreen] scale]; //设置缩放比例，不设置的话，纹理会失真
    
    [self.view.layer addSublayer:layer];
    
    //bind the texture to the output layer
    [self bindRenderLayer:layer];
    
    //load the texture
    NSString *imagePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"logo.avif"];
    UIImage *image = [UIImage imageWithContentsOfFile:imagePath];
    GLuint textureID = [self createTextureWithImage:image];
    
    
    //set the viewport size
    
    glViewport(0, 0, self.drawableWidth, self.drawableHeight);
    
    //compile and link the shaders
    GLuint program = [self programWithShaderName:@"glsl"];
    glUseProgram(program);
    
    //get the parameters from the shader and pass data into them
    GLuint positionSlot = glGetAttribLocation(program, "Position"); //获取顶点着色器的位置
    GLuint textureCoordsSlot = glGetAttribLocation(program, "TextureCoords"); //获取顶点着色器中的纹理坐标

    GLuint textureSlot = glGetUniformLocation(program, "Texture"); //获取片元着色器纹理变量

    //pass the texture ID to the shader program
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureID);
    glUniform1i(textureSlot, 0); // 将textureSlot 赋值为 0, 而 0 与 GL_TEXTURE0 对应,这里如果写1,就是GL_TEXTURE1
    
    //create the vertex buffer
    GLuint vertexBuffer;
    glGenBuffers(1, &vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
    GLsizeiptr bufferSizeBytes = sizeof(SenceVertex) * 4;
    glBufferData(GL_ARRAY_BUFFER, bufferSizeBytes, self.vertices, GL_STATIC_DRAW);
    
    //set the vertex data
    glEnableVertexAttribArray(positionSlot);
    glVertexAttribPointer(positionSlot, 3, GL_FLOAT, GL_FALSE, sizeof(SenceVertex), NULL + offsetof(SenceVertex, positionCoord));
    
    //set the texture data
    glEnableVertexAttribArray(textureCoordsSlot);
    glVertexAttribPointer(textureCoordsSlot, 2, GL_FLOAT, GL_FALSE, sizeof(SenceVertex), NULL + offsetof(SenceVertex, textureCoord));
    
    //start drawing
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    
    //present the renderbuffer
    [self.context presentRenderbuffer:GL_RENDERBUFFER];
    
    //delete the vertex buffer
    glDeleteBuffers(1, &vertexBuffer);
    vertexBuffer = 0;
    
}

//bind the layer where the image will be rendered
- (void)bindRenderLayer:(CALayer <EAGLDrawable> *)layer {
    GLuint frameBuffer; //帧缓冲
    GLuint renderBuffer; //渲染缓冲

    //bind the renderbuffer to the output layer
    glGenRenderbuffers(1, &renderBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, renderBuffer);
    [self.context renderbufferStorage:GL_RENDERBUFFER fromDrawable:layer];
    
    //attach the renderbuffer to the framebuffer
    glGenFramebuffers(1, &frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, renderBuffer);
}

//create a texture from an image
- (GLuint)createTextureWithImage:(UIImage *)image {
    //convert UIImage to CGImageRef
    CGImageRef cgImageRef = [image CGImage];
    GLuint width = (GLuint)CGImageGetWidth(cgImageRef);
    GLuint height = (GLuint)CGImageGetHeight(cgImageRef);
    CGRect rect = CGRectMake(0, 0, width, height);
    
    //draw the image
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    void *imageData = malloc(width * height * 4);
    CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, width * 4, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGContextTranslateCTM(context, 0, height);
    CGContextScaleCTM(context, 1.0f, -1.0f);
    CGColorSpaceRelease(colorSpace);
    CGContextClearRect(context, rect);
    CGContextDrawImage(context, rect, cgImageRef);

    //generate the texture
    GLuint textureID;
    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_2D, textureID);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData); // 将图片数据写入纹理缓存
    
    //set how texels are mapped to pixels
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    
    //unbind
    glBindTexture(GL_TEXTURE_2D, 0);
    
    //release memory
    CGContextRelease(context);
    free(imageData);
    
    return textureID;
}

//attach a vertex shader and a fragment shader to a shader program and return the program id
- (GLuint)programWithShaderName:(NSString *)shaderName {
    //compile the two shaders
    GLuint vertexShader = [self compileShaderWithName:shaderName type:GL_VERTEX_SHADER];
    GLuint fragmentShader = [self compileShaderWithName:shaderName type:GL_FRAGMENT_SHADER];
    
    //attach the shaders to the program
    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, fragmentShader);
    
    //link the program
    glLinkProgram(program);
    
    //check whether the link succeeded
    GLint linkSuccess;
    glGetProgramiv(program, GL_LINK_STATUS, &linkSuccess);
    if (linkSuccess == GL_FALSE) {
        GLchar messages[256];
        glGetProgramInfoLog(program, sizeof(messages), 0, &messages[0]);
        NSString *messageString = [NSString stringWithUTF8String:messages];
        NSAssert(NO, @"program链接失败：%@", messageString);
        exit(1);
    }
    return program;
}

//compile a shader and return the shader id
- (GLuint)compileShaderWithName:(NSString *)name type:(GLenum)shaderType {
    //find the shader file
    NSString *shaderPath = [[NSBundle mainBundle] pathForResource:name ofType:shaderType == GL_VERTEX_SHADER ? @"vsh" : @"fsh"]; // 根据不同的类型确定后缀名
    NSError *error;
    NSString *shaderString = [NSString stringWithContentsOfFile:shaderPath encoding:NSUTF8StringEncoding error:&error];
    if (!shaderString) {
        NSAssert(NO, @"读取shader失败");
        exit(1);
    }
    
    //create a shader object
    GLuint shader = glCreateShader(shaderType);
    
    //get the shader content
    const char *shaderStringUTF8 = [shaderString UTF8String];
    int shaderStringLength = (int)[shaderString length];
    glShaderSource(shader, 1, &shaderStringUTF8, &shaderStringLength);
    
    //compile the shader
    glCompileShader(shader);
    
    //check whether the shader compiled successfully
    GLint compileSuccess;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &compileSuccess);
    if (compileSuccess == GL_FALSE) {
        GLchar messages[256];
        glGetShaderInfoLog(shader, sizeof(messages), 0, &messages[0]);
        NSString *messageString = [NSString stringWithUTF8String:messages];
        NSAssert(NO, @"shader编译失败：%@", messageString);
        exit(1);
    }
    
    return shader;
}


#pragma mark -
#pragma mark - public methods



#pragma mark -
#pragma mark - getters and setters
//get the renderbuffer width
- (GLint)drawableWidth {
    GLint backingWidth;
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
    
    return backingWidth;
}

//get the renderbuffer height
- (GLint)drawableHeight {
    GLint backingHeight;
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);
    
    return backingHeight;
}

#pragma mark -
#pragma mark - life cycle
- (void)dealloc {
    if ([EAGLContext currentContext] == self.context) {
        [EAGLContext setCurrentContext:nil];
    }
    //free the array memory in the struct, needs manual free
    if (_vertices) {
        free(_vertices);
        _vertices = nil;
    }
}

@end