需要简单OpenGL ES 2.0代码的帮助

Question

我在OpenGL方面是个十足的白痴，我不明白为什么我的代码不能工作，只有清晰的颜色显示出来。我正在尝试在iOS上设置一些简单的渲染。有人能帮帮我吗？

我的主要场景代码是：

//
//  Scene.m
#import "Scene.h"
GLfloat vertices[] = {
    0.0, 0.0,
    1.0, 0.0,
    0.0, 1.0,
    1.0, 1.0
};
@implementation Scene
+(Class)layerClass {
    return [CAEAGLLayer class];
}
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        CAEAGLLayer *glLayer = (CAEAGLLayer *)self.layer;
        glLayer.opaque = YES;
        glLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:FALSE], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
        context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
        if (!context) {
            NSLog(@"Failed to create 2.0 context");
            exit(1);
        }
        [EAGLContext setCurrentContext:context];

        GLuint framebuffer, colorRenderbuffer;
        glGenFramebuffers(1, &framebuffer);
        glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
        glGenRenderbuffers(1, &colorRenderbuffer);
        glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
        [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:glLayer];
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
        GLuint vbo;
        glGenBuffers(1, &vbo);
        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
        GLuint program = [self loadShaders:@"Test.vp" frag:@"Test.fp"];
        positionIndex = glGetAttribLocation(program, "position");
        mvpIndex = glGetUniformLocation(program, "mvp");
        glLinkProgram(program); //added this
        GLint param;
        glGetProgramiv(program, GL_LINK_STATUS, &param);
        if (param == GL_FALSE) {
            NSLog(@"Failed to link the program");
            exit(1);
        }
        glUseProgram(program);
        CADisplayLink *displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(render:)];
        [displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    }
    return self;
}
-(void)render:(CADisplayLink *)_displayLink {
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glEnableVertexAttribArray(positionIndex);
    glVertexAttribPointer(positionIndex, 2, GL_FLOAT, GL_FALSE, 0, (GLvoid *)0);
    GLfloat mvp[] = {
        1, 0, 0, 0,
        0, 1, 0, 0,
        0, 0, 1, 0,
        0, 0, 0, 1
    };
    glUniformMatrix4fv(mvpIndex, 1, GL_FALSE, mvp);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    [context presentRenderbuffer:GL_RENDERBUFFER];
    glDisableVertexAttribArray(positionIndex);
}
-(GLuint)loadShaders:(NSString *)vertShader frag:(NSString *)fragShader {
    NSString *vertPath = [[NSBundle mainBundle] pathForResource:[vertShader stringByDeletingPathExtension] ofType:@"vp"];
    NSString *fragPath = [[NSBundle mainBundle] pathForResource:[fragShader stringByDeletingPathExtension] ofType:@"fp"];
    if (!vertPath || !fragPath) {
        NSLog(@"Failed to find paths of shaders");
        exit(1);
    }
    NSError *error;
    const GLchar* vertSource = [[NSString stringWithContentsOfFile:vertPath encoding:NSUTF8StringEncoding error:&error] UTF8String];
    const GLchar* fragSource = [[NSString stringWithContentsOfFile:fragPath encoding:NSUTF8StringEncoding error:&error] UTF8String];
    if (!vertSource || !fragSource) {
        NSLog(@"Faild to load shader sourcesn%@", [error localizedDescription]);
        exit(1);
    }
    GLuint vert, frag;
    vert = glCreateShader(GL_VERTEX_SHADER);
    frag = glCreateShader(GL_FRAGMENT_SHADER);
    GLint length = strlen(vertSource);
    glShaderSource(vert, 1, &vertSource, &length);
    length = strlen(fragSource);
    glShaderSource(frag, 1, &fragSource, &length);
    glCompileShader(vert);
    glCompileShader(frag);
    GLint success;
    glGetShaderiv(vert, GL_COMPILE_STATUS, &success);
    if (success == GL_FALSE) {
        GLchar messages[256];
        glGetShaderInfoLog(vert, sizeof(messages), 0, &messages[0]);
        NSLog(@"Failed to compile vertex shadern%@", [NSString stringWithUTF8String:messages]);
        exit(1);
    }
    glGetShaderiv(frag, GL_COMPILE_STATUS, &success);
    if (success == GL_FALSE) {
        GLchar messages[256];
        glGetShaderInfoLog(frag, sizeof(messages), 0, &messages[0]);
        NSLog(@"Failed to compile fragment shadern%@", [NSString stringWithUTF8String:messages]);
        exit(1);
    }
    GLuint prog = glCreateProgram();
    glAttachShader(prog, vert);
    glAttachShader(prog, frag);
    //Removed glLinkProgram()
    return prog;
}
@end

着色器代码为：

attribute vec2 position;
uniform mat4 mvp;
void main(void) {
    gl_Position = mvp * vec4(position.xy, -1.0, 1.0);
}

和

void main() {
    gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
}

提前感谢

Answer 1

glEnableVertexAttribArray(positionIndex);
glVertexAttribPointer(positionIndex, 2, GL_FLOAT, GL_FALSE, 0, vertices);

此行不正确：

glDisableVertexAttribArray(positionIndex);

在使用之前不要禁用它，否则你会丢失

此外，由于您正在为verts使用vbo，因此不需要这样做：

glVertexAttribPointer(positionIndex, 2, GL_FLOAT, GL_FALSE, 0, vertices);

只需将其切换为：

glVertexAttribPointer(positionIndex, 2, GL_FLOAT, GL_FALSE, 0, (void*)0);

你有一个绑定到GPU的vbo，它将使用该缓冲区进行绘制。使用glVertexAttribPointer将偏移量定义到vbo中，它将找到给定属性的第一个元素。

@kibab我为vbo提出的建议是正确的。

由于他的属性未绑定到着色器，他收到了EXC_BAD_ACCESS。请参阅下面的评论。至于mvp，你又错了。mvp旨在将点转换为-1.0, -1.0到1.0, 1.0的坐标系。这意味着他的顶点应该显示给定的值。

请参阅http://flylib.com/books/2/789/1/html/2/images/03fig02.jpg.

此外，更改z坐标对您没有任何帮助。将你的垂直线从-1.0，-1.0开始，然后转到1.0，1.0一个全屏框，这样我们就可以在屏幕上看到一些东西。

假设您没有使用任何苹果提供的gl类，则不会设置glViewPort。

尝试使用视图边界的大小

glViewport(0, 0, bouds.width, bounds.height);

此外，请将你的verts设置为0.0 z，而不是-1.0

也让我们试试这个，只是想弄清楚哪里出了问题！尽量不要使用顶点缓冲区对象，而是像这样直接传递它。另外，现在不要担心禁用您的属性，让我们先在屏幕上显示一些内容。

GLfloat     vertices[] = {  
            -1.0f,  -1.0f,  0.0f,
            1.0f,   -1.0f , 0.0f,
            -1.0f,  1.0f ,  0.0f,
            1.0f,   1.0f ,  0.0f,};
        glVertexAttribPointer(positionIndex,3,GL_FLOAT,0,0,vertices);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);