0013--GLSL和GLKit的索引绘制

[toc]

前言

OpenGL提供了一些绘图函数。到目前为止我们使用的glDrawArrays绘图函数属于”顺序绘制”。这意味着顶点缓冲区从指定的偏移量开始被扫描，每X（点为1，直线为2等）个顶点构成一个图元。这样使用起来非常方便，缺点是当多个图元共用一个顶点时，这个顶点必须在顶点缓冲区中出现多次。也就是说，这些顶点没有共享的概念。属于”索引绘制”的函数则提供这种共享机制。我们除了一个顶点缓存区外，还有一个索引缓存区用来存放顶点的索引值。索引缓存区的扫描和顶点缓存区类似，以每X个索引对应的顶点构成一个基本图元。共享机制在提高内存使用效率上非常重要，因为计算机中的绝大多数图形对象都是三角形网格构成的，这些三角形有很多都是共用顶点。

• 顺序绘制,一个金字塔,需要传入18个顶点的信息

image.png

• 索引绘制

1.只需要传入5个顶点的位置和绘制不同面的连接方式.

image

GLSL绘制金字塔

• 0.vsh,fsh自定义着色器的代码

1..vsh

...
uniform mat4 projectionMatrix;
uniform mat4 modelViewMatrix;
...
void main(){
  ...
  
  vec4 vPos;
  vPos = projectionMatrix * modelViewMatrix *    position;
 gl_Position = vPos;
}

2.fsh

varying lowp vec4 varyColor;

void main(){
    gl_FragColor = varyColor;
}

增加两个uniform修饰的4x4矩阵,模型矩阵和投影矩阵.
将它们的相乘之后的结果返回给gl_Position;

• 1.设置图层

- (void)setUpLayer{
    self.myEagLayer = (CAEAGLLayer *)self.layer;
    [self setContentScaleFactor:[[UIScreen mainScreen] scale]];
    self.myEagLayer.opaque = YES;
    NSDictionary *dict = @{
        kEAGLDrawablePropertyRetainedBacking:@(NO),
        kEAGLDrawablePropertyColorFormat:kEAGLColorFormatRGBA8
    };
    self.myEagLayer.drawableProperties = dict;
    
}
+ (Class)layerClass{
    return [CAEAGLLayer class];
}

• 2.设置上下文

- (void)setContext{
    
    EAGLContext *context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];
    if (!context){
        NSLog(@"context init error");
        return;
    }
    if (![EAGLContext setCurrentContext:context]){
        NSLog(@"setCurrentContext error");
        return;
    }
    self.myContext = context;
}

• 3.清空缓冲区

- (void)deleBuffer{
    glDeleteBuffers(1, &_myColorRenderBuffer);
    self.myColorRenderBuffer = 0;
    glDeleteBuffers(1, &_myColorFrameBuffer);
    self.myColorFrameBuffer = 0;
}

• 4. 设置renderBuffer

- (void)setUpRenderBuffer{
    GLuint buffer;
    glGenRenderbuffers(1, &buffer);
    self.myColorRenderBuffer = buffer;
    glBindRenderbuffer(GL_RENDERBUFFER, self.myColorRenderBuffer);
    [self.myContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:self.myEagLayer];
}

• 5. 设置renderBuffer

- (void)setUpFrameBuffer{
    GLuint buffer;
    glGenFramebuffers(1, &buffer);
    self.myColorFrameBuffer = buffer;
    glBindFramebuffer(GL_FRAMEBUFFER, self.myColorFrameBuffer);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, self.myColorRenderBuffer);
}

• 开启绘制

1. 加载链接自定义着色器

//清屏设置颜色
    glClearColor(0.0, 0.0, 0.3, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    
    //调整视口
    CGFloat scale = [[UIScreen mainScreen] scale];
    glViewport(self.frame.origin.x * scale, self.frame.origin.y * scale, self.frame.size.width * scale, self.frame.size.height * scale);
    //获取顶点着色器程序和片段着色器程序的文件路径
    NSString *shaderVfile = [[NSBundle mainBundle] pathForResource:@"shaderV" ofType:@"vsh"];
    NSString *shaderFfile = [[NSBundle mainBundle] pathForResource:@"shaderF" ofType:@"fsh"];
    //存在清空
    if (self.myProgram){
        glDeleteProgram(self.myProgram);
        self.myProgram = 0;
    }
    //加载 绑定 链接 使用
//    self.myProgram =  [self loadShader:shaderVfile frag:shaderFfile];
    self.myProgram = [GLESUtils loadProgram:shaderVfile withFragmentShaderFilepath:shaderFfile];
    //链接
    glLinkProgram(self.myProgram);
    GLint linkSuccess;
    
    //获取链接状态
    
    glGetProgramiv(self.myProgram, GL_LINK_STATUS, &linkSuccess);
    if (linkSuccess == GL_FALSE){
        GLchar messages[1024];
        glGetProgramInfoLog(self.myProgram, sizeof(messages), 0, &messages[0]);
        NSString *messageString = [NSString stringWithUTF8String:messages];
        NSLog(@"error%@", messageString);
        
        return ;
    }
    NSLog(@"link success");
    glUseProgram(self.myProgram);

• 清屏设置颜色
• 调整视口
• 获取顶点着色器程序和片段着色器程序的文件路径
• 加载 绑定 链接 使用

2. 传入顶点数据和颜色值

 // 创建顶点数组和索引数组
    GLfloat attArr[] = {
       -0.5f, 0.5f, 0.0f,      1.0f, 0.0f, 1.0f, //左上0
       0.5f, 0.5f, 0.0f,       1.0f, 0.0f, 1.0f, //右上1
       -0.5f, -0.5f, 0.0f,     1.0f, 1.0f, 1.0f, //左下2
       0.5f, -0.5f, 0.0f,      1.0f, 1.0f, 1.0f, //右下3
       0.0f, 0.0f, 1.0f,       0.0f, 1.0f, 0.0f, //顶点4
        
    };
    //索引
    GLuint indices[] = {
       0, 3, 2,
       0, 1, 3,
       0, 2, 4,
       0, 4, 1,
       2, 3, 4,
       1, 4, 3,
    };
    
    // 判断顶点缓冲区是否为空,如果为空则申请一个缓冲区标识
    if (self.myVertices == 0){
        glGenBuffers(1, &_myVertices);
    }
    //处理顶点数据
    glBindBuffer(GL_ARRAY_BUFFER, _myVertices);
    glBufferData(GL_ARRAY_BUFFER, sizeof(attArr), attArr, GL_DYNAMIC_DRAW);
    // 获取文件中position
    GLuint position = glGetAttribLocation(self.myProgram, "position");
    //打开position
    glEnableVertexAttribArray(position);
    //读取方式
    glVertexAttribPointer(position, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat)*6, NULL);
    

   // 获取文件中positionColor
    GLuint positionColor = glGetAttribLocation(self.myProgram, "positionColor");
    //打开positionColor
    glEnableVertexAttribArray(positionColor);
    //读取方式
    glVertexAttribPointer(positionColor, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat)*6,(float *)NULL + 3);

3. 模型矩阵和投影矩阵的值设置

//获取myProgram中的projectionMatrix、modelViewMatrix
    GLuint projectionMatrixSlot = glGetUniformLocation(self.myProgram, "projectionMatrix");
    GLuint modelViewMatrixSlot = glGetUniformLocation(self.myProgram, "modelViewMatrix");
    float width = self.frame.size.width;
    float height = self.frame.size.height;
    
    KSMatrix4 _projectionMatrix;
    ksMatrixLoadIdentity(&_projectionMatrix);
    float aspect = width/height;
    
    ksPerspective(&_projectionMatrix, 30, aspect, 5.0f, 20.f);
    glUniformMatrix4fv(projectionMatrixSlot, 1, GL_FALSE, (GLfloat *)&_projectionMatrix.m[0][0]);
    
    KSMatrix4 _modelViewMatrix;
    ksMatrixLoadIdentity(&_modelViewMatrix);
    ksTranslate(&_modelViewMatrix, 0, 0, -10.0);
    
    KSMatrix4 _rotationMatrix;
    ksMatrixLoadIdentity(&_rotationMatrix);
    ksRotate(&_rotationMatrix, xDegree, 1.0, 0.0, 0.0);
    ksRotate(&_rotationMatrix, yDegree, 0.0, 1.0, 0.0);
    ksRotate(&_rotationMatrix, zDegree, 0.0, 0.0, 1.0);
    
    ksMatrixMultiply(&_modelViewMatrix, &_rotationMatrix, &_modelViewMatrix);
    
    glUniformMatrix4fv(modelViewMatrixSlot, 1, GL_FALSE, (GLfloat *)&_modelViewMatrix.m[0][0]);

void glUniformMatrix4fv(GLint location, GLsizei count, GLboolean transpose, const GLfloat *value);
参数列表：
location:指要更改的uniform变量的位置
count:更改矩阵的个数
transpose:是否要转置矩阵，并将它作为uniform变量的值。必须为GL_FALSE
value:执行count个元素的指针，用来更新指定uniform变量

4. 开始正背面剔除 颜色混合 开始绘制

glEnable(GL_CULL_FACE);

    glEnable(GL_BLEND);
    //2.开启组合函数 计算混合颜色因子
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    
    glDrawElements(GL_TRIANGLES, sizeof(indices)/sizeof(indices[0]), GL_UNSIGNED_INT, indices);
    [self.myContext presentRenderbuffer:GL_RENDERBUFFER];

使用索引绘图
void glDrawElements(GLenum mode,GLsizei count,GLenum type,const GLvoid * indices);
参数列表：
mode:要呈现的画图的模型
GL_POINTS
GL_LINES
GL_LINE_LOOP
GL_LINE_STRIP
GL_TRIANGLES
GL_TRIANGLE_STRIP
GL_TRIANGLE_FAN
count:绘图个数
type:类型
GL_BYTE
GL_UNSIGNED_BYTE
GL_SHORT
GL_UNSIGNED_SHORT
GL_INT
GL_UNSIGNED_INT
indices：绘制索引数组

5.旋转动画

- (IBAction)roteXAction:(UIButton *)sender {
    if (!myTimer){
        myTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(roteAction) userInfo:nil repeats:YES];
    }
    bX = !bX;
}
- (IBAction)roteYAction:(UIButton *)sender {
    if (!myTimer){
        myTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(roteAction) userInfo:nil repeats:YES];
    }
    bY = !bY;
}

- (IBAction)roteZAction:(UIButton *)sender {
    if (!myTimer){
        myTimer = [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(roteAction) userInfo:nil repeats:YES];
    }
    bZ = !bZ;
}

- (void)roteAction{
    xDegree += bX*5;
    yDegree += bY*5;
    zDegree += bZ*5;
    [self render];
}

点击绕对应轴旋转,再次点击停止.
如果停止X轴旋转，X = 0则度数就停留在暂停前的度数.

效果图:

image

demo

GLKit绘制金字塔

• 1.初始化

1. OPVertex保存顶点坐标和颜色值

typedef struct OPVertex{
    GLKVector3 positionCoord;
    GLKVector3 colorCoord;
}OPVertex;

• 2.设置上下文,开启深度测试

- (void)setUpcontext{
    self.myContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES3];
    GLKView *view = (GLKView *)self.view;
    view.context = self.myContext;
    view.drawableColorFormat = GLKViewDrawableColorFormatRGBA8888;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat24;
   BOOL isSuc =  [EAGLContext setCurrentContext:self.myContext];
    if (!isSuc){
        
        NSLog(@"setCurrentContext error");
        return;
    }
    glEnable(GL_DEPTH_TEST);
}

• 3. 开始绘制

1. 设置顶点数据和索引绘制数组

self.vertices = (OPVertex *)malloc(sizeof(OPVertex)*kCount);
    self.vertices[0] = (OPVertex){{-0.5f, 0.5f, 0.0f},{1.0f, 0.0f, 1.0f}};
    self.vertices[1] = (OPVertex){{0.5f, 0.5f, 0.0f},{1.0f, 0.0f, 1.0f}};
    self.vertices[2] = (OPVertex){{-0.5f, -0.5f, 0.0f},{1.0f, 1.0f, 1.0f}};
    self.vertices[3] = (OPVertex){{0.5f, -0.5f, 0.0f},{1.0f, 1.0f, 1.0f}};
    self.vertices[4] = (OPVertex){{0.0f, 0.0f, 1.0f},{0.0f, 1.0f, 0.0f}};
    //绘图索引
    GLuint indices[] =
       {
           0, 3, 2,
           0, 1, 3,
           0, 2, 4,
           0, 4, 1,
           2, 3, 4,
           1, 4, 3,
       };

2. 计算顶点个数

self.count = sizeof(indices) /sizeof(GLuint);

3. 将顶点数组放入数组缓冲区中 GL_ARRAY_BUFFER

 GLuint buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(OPVertex)*kCount, self.vertices, GL_STATIC_DRAW);

4. 将索引数组存储到索引缓冲区 GL_ELEMENT_ARRAY_BUFFER

GLuint bufferIndex;
    glGenBuffers(1, &bufferIndex);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bufferIndex);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

5. 使用顶点数据

glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 6, NULL);

6. 使用颜色数据

glEnableVertexAttribArray(GLKVertexAttribColor);
    glVertexAttribPointer(GLKVertexAttribColor, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat)*6, (GLfloat *)NULL + 3);

7. 初始化着色器

 self.mEffect = [[GLKBaseEffect alloc]init];

8. 创建投影视图矩阵

CGSize size = self.view.bounds.size;
    float aspect = fabs(size.width / size.height);
    GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(90.0), aspect, 0.1f, 100.0);
    projectionMatrix = GLKMatrix4Scale(projectionMatrix, 1.0f, 1.0f, 1.0f);
    self.mEffect.transform.projectionMatrix = projectionMatrix;

9. 模型视图矩阵

GLKMatrix4 modelViewMatrix = GLKMatrix4Translate(GLKMatrix4Identity, 0.0f, 0.0f, -2.0f);
    self.mEffect.transform.modelviewMatrix = modelViewMatrix;

10. 创建一个定时器用来旋转金字塔

[NSTimer scheduledTimerWithTimeInterval:0.1 repeats:YES block:^(NSTimer * _Nonnull timer) {
        self.XDegree += 0.1f * self.XB;
        self.YDegree += 0.1f * self.YB;
        self.ZDegree += 0.1f * self.ZB ;
    }];

11. 开始绘制

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect{
    glClearColor(0.1f, 0.3f, 0.5f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    [self.effect prepareToDraw];
    glDrawElements(GL_TRIANGLES, self.count, GL_UNSIGNED_INT, 0);
}

demo

效果图:

image

总结

image

1. API的工作

• 设置图层
• 设置上下文
• 清空缓冲区
• 设置renderBuffer
• 设置FrameBuffer

2. 绘制

• 把顶点数据,颜色数据等从CPU内存复制到GPU上
• 在可编程顶点着色器中对顶点坐标纹理坐标,颜色数据,模型矩阵,投影矩阵等输入.
• 输出 gl_position等
• 然后信息图元装配,视口变换等,生成一组二维数据传递给片段着色器.
• 片段着色器输出gl_Fragcolor
• 最后通过片段操作
• 数据放在帧缓存区

在开发中,基本上是按照这种模式进行代码编写.