在opengles中渲染三角形

Question

我发现用opengles开始真的很难。我在网上寻找教程。发现飞利浦Rideout的一本免费书，尝试了几个章节，但由于缺乏良好的C ++技能，我把它留在中间。然后尝试了Ray Wenderlich的教程并且使用了着色器并且无法完成一个非常简单的教程。现在，我和Jeff Lamarche的老博客一起挥之不去。我知道有一个非常好的面向对象框架，称为COCOS2D，几乎可以完成2D游戏和图形所需的一切，但我想在实际尝试COCOS2D之前做好基础。但是，似乎我永远不会到达那里。我一个接一个地遇到麻烦，我无法找到解决办法。所以，我一次又一次地堆积溢出来清除我的误解。您的帮助和支持将始终帮助我清除代码中的错误，当然也可以消除我的误解。

我在OpenGLES中遇到一个非常简单的三角形问题。此示例使用OpenGLES 1.0。在我的视图中渲染图形的代码就是这样，

struct Vertex3D{
    GLfloat x;
    GLfloat y;
    GLfloat z;

};


struct Triangle3D{
    Vertex3D v1;
    Vertex3D v2;
    Vertex3D v3;

};


static inline Triangle3D Triangle3DMake(Vertex3D vertex1, Vertex3D vertex2, Vertex3D vertex3){
    Triangle3D triangle;
    triangle.v1 = vertex1;
    triangle.v2 = vertex2;
    triangle.v3 = vertex3;
    return triangle;
};

static inline Vertex3D vertex3DMake(GLfloat x, GLfloat y, GLfloat z){
    Vertex3D vertex;
    vertex.x = x;
    vertex.y = y;
    vertex.z = z;
    return vertex;
}


static inline GLfloat Vertex3DCalculateDistanceBetweemVertices(Vertex3D first, Vertex3D second){
    GLfloat deltaX = second.x - first.x;
    GLfloat deltaY = second.y - first.y;
    GLfloat deltaZ = second.z - first.z;
    return sqrtf(powf(deltaX, 2) + powf(deltaY, 2) + powf(deltaZ, 2));
}


@implementation GLView{
    GLuint renderbuffer;
    GLuint framebuffer;
    EAGLContext *_context;
    CAEAGLLayer *layer;
    GLuint depthbuffer;
}

+(Class)layerClass{
    return [CAEAGLLayer class];
}

-(void)setUpLayer{
    layer = (CAEAGLLayer*)super.layer;
}

-(void)setUpContext{
    EAGLRenderingAPI api = kEAGLRenderingAPIOpenGLES1;
    _context = [[EAGLContext alloc] initWithAPI:api];
    if(!_context){
        NSLog(@"Could not create context");
        abort();
    }

    if(![EAGLContext setCurrentContext:_context]){
        NSLog(@"Could not set current context");
        abort();
    }
}

-(void)setUpRenderBuffer{
    glGenRenderbuffersOES(1, &renderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, renderbuffer);

    glGenRenderbuffers(1, &depthbuffer);
    glBindRenderbufferOES(GL_DEPTH_COMPONENT16_OES, depthbuffer);
    [_context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:layer];
    [_context renderbufferStorage:GL_DEPTH_COMPONENT16_OES fromDrawable:layer];
}

-(void)setUpFrameBuffer{
    glGenFramebuffersOES(1, &framebuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, renderbuffer);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_DEPTH_COMPONENT16_OES, depthbuffer);
}

-(void)render{
    Vertex3D    vertex1 = vertex3DMake(0,1,0);
    Vertex3D    vertex2 = vertex3DMake(1.0, 0.0, 0);
    Vertex3D    vertex3 = vertex3DMake(-1.0, 0.0, 0.);
    Triangle3D  triangle = Triangle3DMake(vertex1, vertex2, vertex3);
    glViewport(0, 0, self.bounds.size.width, self.bounds.size.height);
    glClearColor(0.7, 0.7, 0.7, 1.0);
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    glEnableClientState(GL_VERTEX_ARRAY);
    glColor4f(1.0, 0.0, 0.0, 1.0);
    glVertexPointer(3, GL_FLOAT, 0, &triangle);
    glDrawArrays(GL_TRIANGLES, 0, 9);
    [_context presentRenderbuffer:GL_RENDERBUFFER_OES];
    glDisableClientState(GL_VERTEX_ARRAY);


}
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setUpLayer];
        [self setUpContext];
        [self setUpRenderBuffer];
        [self setUpFrameBuffer];

        [self render];
    }
    return self;
}

此代码产生的数字如下图所示;

因为我正在使用带有（1,0），（ - 1,0），（1,0）的2D坐标，所以我假设它应该给我这样的图形;

我确信我做的事情非常小。如果有人能指出我，那对我来说将是一个很大的帮助。再次感谢你。

Answer 1

看起来你只是渲染了太多的顶点，而OpenGL正在读取你的顶点数组的末尾到未初始化的内存。这条线

glDrawArrays(GL_TRIANGLES, 0, 9);

应该是

glDrawArrays(GL_TRIANGLES, 0, 3);

如果您只想绘制一个三角形。第三个参数是要渲染的顶点总数。