objective-c - 需要有关简单 OpenGL ES 2.0 代码的帮助

Question

我在 OpenGL 方面完全是个白痴，我无法弄清楚为什么我的代码不起作用，只显示清晰的颜色。我正在尝试在 iOS 上设置一些简单的渲染。有人可以帮助我吗？

我的主场景代码是:

//
//  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 sources\n%@", [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 shader\n%@", [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 shader\n%@", [NSString stringWithUTF8String:messages]);
        exit(1);
    }

    GLuint prog = glCreateProgram();
    glAttachShader(prog, vert);
    glAttachShader(prog, frag);

    //Removed glLinkProgram()

    return prog;
}
@end

着色器代码是:

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);
}

提前致谢

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，否则你会失去它

另外，因为你正在为你的顶点使用 vbo，所以你不需要这样做:

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);

您有一个绑定(bind)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(bind)到他的着色器，他正在接收 EXC_BAD_ACCESS。请参阅下面的评论。至于mvp，你又错了。 mvp的意思是将点转换成-1.0, -1.0的坐标系，到1.0, 1.0。这意味着他的顶点应该显示给定的值。

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

同时更改 z 坐标对您没有任何作用。将您的顶点更改为从 -1.0、-1.0 开始并转到 1.0、1.0 一个全屏框，这样我们就可以在屏幕上显示一些东西。

假设您没有使用任何苹果提供的 gl 类，您的 glViewPort 没有被设置。

尝试使用 View 的边界大小

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

另外请把你的顶点放在 0.0 z 而不是 -1.0

我们也试试这个，看看哪里出了问题! 尽量不要使用顶点缓冲对象并像这样直接传递它。 现在也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);