OpenGL ES畫板

一、概述

利用自定義頂點和片元著色器渲染，並且設置圖片紋理顏色為畫筆顏色

二、核心代碼

- (void)renderLineFromPoint:(CGPoint)start toPoint:(CGPoint)end
{
    //頂點緩存區
    static GLfloat *vertexBuffer = NULL;
    //頂點Max
    static NSUInteger vertexMax = 64;
    //頂點個數
    NSUInteger vertexCount = 0,count;
    CGFloat scale = self.contentScaleFactor;
    
    //點到像素轉換：乘以比例因數
    start.x *= scale;
    start.y *= scale;
    end.x *= scale;
    end.y *= scale;
    
    //開闢頂點緩存區
    if (vertexBuffer == NULL) {
        vertexBuffer = malloc(vertexMax*2*sizeof(GLfloat));
    }
    
    //求得兩點之間的距離
    float seq = sqrtf((end.x-start.x)*(end.x-start.x)+(end.y-start.y)*(end.y-start.y));
    /*向上取整：求得距離要產生多少個點
     kBrushPixelStep值越大，筆觸越細；值越小，筆觸越粗
     */
    NSInteger pointCount = ceil(seq/kBrushPixelStep);
    count = MAX(pointCount, 1);
    
    for (int i = 0; i < count; i++) {
        if (vertexCount == vertexMax) {
            //修改2倍增長
            vertexMax = 2*vertexMax;
            vertexBuffer = realloc(vertexBuffer, vertexMax*2*sizeof(GLfloat));
        }
        
        //計算兩個之間的距離有多少個點，並存儲在頂點緩存區中
        vertexBuffer[2*vertexCount+0] = start.x+(end.x-start.x)*((GLfloat)i/(GLfloat)count);
        vertexBuffer[2*vertexCount+1] = start.y+(end.y-start.y)*((GLfloat)i/(GLfloat)count);
        
        vertexCount++;
    }
    
    //綁定頂點數據
    glBindBuffer(GL_ARRAY_BUFFER, vboID);
    //將數據從CPU中複製到GPU中提供給OpenGL使用
    glBufferData(GL_ARRAY_BUFFER, vertexCount*2*sizeof(GLfloat), vertexBuffer, GL_DYNAMIC_DRAW);
    
    //啟用指定屬性
    glEnableVertexAttribArray(ATTRIB_VERTEX);
    //鏈接頂點屬性
    glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, GL_FALSE, 2*sizeof(GLfloat), 0);
    
    //使用數據匯流排：傳遞頂點數據到頂點著色器
    glUseProgram(program[PROGRAME_POINT].id);
    //繪製頂點：繪製模型、起始點、頂點個數
    glDrawArrays(GL_POINTS, 0, (int)vertexCount);
    //綁定渲染緩存區到特定標誌符上
    glBindRenderbuffer(GL_RENDERBUFFER, viewRenderBuffer);
    //開始渲染
    [context presentRenderbuffer:GL_RENDERBUFFER];
    
}

- (textureInfo_t)textureFromName:(NSString *)name
{
    CGImageRef brushImage;
    CGContextRef brushContext;
    GLubyte *brushData;
    size_t width, height;
    GLuint texID;
    textureInfo_t texture;
    
    brushImage = [UIImage imageNamed:name].CGImage;
    width = CGImageGetWidth(brushImage);
    height = CGImageGetHeight(brushImage);
    //開闢紋理圖片記憶體
    brushData = (GLubyte *)calloc(width*height*4, sizeof(GLubyte));
    
    /*創建點陣圖上下文
     參數：圖片記憶體地址、圖片寬、圖片高、像素組件位數（一般設置8），每一行所占比特數、顏色空間、顏色通道
     */
    brushContext = CGBitmapContextCreate(brushData, width, height, 8, width*4, CGImageGetColorSpace(brushImage), kCGImageAlphaPremultipliedLast);
    
    //繪圖
    CGContextDrawImage(brushContext, CGRectMake(0, 0, (CGFloat)width, (CGFloat)height), brushImage);
    //釋放上下文
    CGContextRelease(brushContext);
    
    //申請紋理標誌符
    glGenTextures(1, &texID);
    //綁定紋理
    glBindTexture(GL_TEXTURE_2D, texID);
    //設置紋理屬性：縮小濾波器、線性濾波器
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    /*生成2D紋理圖片
     參數：紋理目標、圖像級別（0為基本級別）、顏色組件（GL_RGBA、GL_ALPHA）、圖像寬、圖像高、邊框寬度（一般為0）、像素數據顏色格式、像素數據類型、記憶體中指向圖像數據指針
     */
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (int)width, (int)height, 0, GL_RGBA, GL_UNSIGNED_BYTE, brushData);
    
    free(brushData);
    
    //配置紋理屬性
    texture.id = texID;
    texture.width = (int)width;
    texture.height = (int)height;
    
    return texture;
}

- (void)setupShaders
{
    for (int i = 0; i < NUM_PROGRAMS; i++) {
        
        //讀取頂點著色器程式
        char *vsrc = readFile(pathForResource(program[i].vert));
        //讀取片元著色器程式
        char *fsrc = readFile(pathForResource(program[i].frag));
        NSString *vsrcStr = [[NSString alloc] initWithBytes:vsrc length:strlen(vsrc)-1 encoding:NSUTF8StringEncoding];
        NSString *fsrcStr = [[NSString alloc] initWithBytes:fsrc length:strlen(fsrc)-1 encoding:NSUTF8StringEncoding];
        NSLog(@"vsrcStr------%@", vsrcStr);
        NSLog(@"fsrcStr------%@", fsrcStr);
        
        GLsizei attribCt = 0;
        GLchar *attribUsed[NUM_ATTRIBS];
        GLint attrib[NUM_ATTRIBS];
        GLchar *attribName[NUM_ATTRIBS] = {
            "inVertex"
        };
        
        const char *uniformName[NUM_UNIFORMS] = {
            "MVP","pointSize","vertexColor", "texture"
        };
        
        for (int j = 0; j < NUM_ATTRIBS; j++) {
            if (strstr(vsrc, attribName[j])) {
                attrib[attribCt] = j;
                attribUsed[attribCt++] = attribName[j];
            }
        }
        
        //program處理：創建、鏈接、生成
        glueCreateProgram(vsrc, fsrc, attribCt, (const char **)&attribUsed[0], attrib, NUM_UNIFORMS, &uniformName[0], program[i].uniform, &program[i].id);
        
        free(vsrc);
        free(fsrc);
        
        if (i == PROGRAME_POINT) {
            glUseProgram(program[PROGRAME_POINT].id);
           //為當前程式指定uniform變數
            glUniform1i(program[PROGRAME_POINT].uniform[UNIFORM_TEXTURE], 0);
            
            //設置正射投影矩陣
            GLKMatrix4 projectionMatrix = GLKMatrix4MakeOrtho(0, backingWidth, 0, backingHeight, -1, 1);
            //創建模型視圖矩陣：單元矩陣
            GLKMatrix4 modelViewMatrix = GLKMatrix4Identity;
            //正射投影矩陣與模型視圖矩陣相乘，結果保存在MVPMatrix矩陣中
            GLKMatrix4 MVPMatrix = GLKMatrix4Multiply(projectionMatrix, modelViewMatrix);
           
           /*為當前程式指定Uniform變數值
            參數：指明要更改的Uniform變數的位置、將要被修改的矩陣的數量、矩陣值被載入變數時是否要對舉證進行變換（如轉置）、將要用於更新uniform變數MVP的數組指針
            */
            glUniformMatrix4fv(program[PROGRAME_POINT].uniform[UNIFORM_MVP], 1, GL_FALSE, MVPMatrix.m);
           //為當前程式對象Uniform變數的pointSize賦值
            glUniform1f(program[PROGRAME_POINT].uniform[UNIFORM_POINT_SIZE], brushTexture.width/kBrushScale);
            //為當前程式對象Uniform變數頂點顏色賦值
            glUniform4fv(program[PROGRAME_POINT].uniform[UNIFORM_VERTEX_COLOR], 1, brushColor);
            
        }
    }
    
    glError();
}

三、效果圖

GitHub