ios - 使用指针设置顶点不起作用

Question

我目前正在使用 OpenGL ES 2.0 研究一些 OpenGL 基础知识。

如果我将顶点设置为顶部的常量，则会绘制三角形；如果我尝试使用指针在方法中设置它们，则不会绘制任何内容。我错过了什么？

#import "CometGLViewController.h"

typedef struct {
    float Position[3];
    float Color[4];
} Vertex;

//vertices store information for each "point" used to draw a triangle
Vertex* Vertices; // NOT DRAWING
//const Vertex Vertices[] = {
//    {{0, 0, 0},{0, 0, 0, 1}},
//    {{1, 1, 0}, {1, 0, 0, 1}},
//    {{0, 1, 0}, {1, 0, 0, 1}},
//}; // THIS WORKS

//Used to reuse vertices
const GLubyte Indices[] = {
    0, 1, 2,
};

...一些其他的东西

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];

    if (!self.context) {
        NSLog(@"Failed to create ES context");
    }

    GLKView *view = (GLKView *)self.view;
    view.context = self.context;
    view.drawableMultisample = GLKViewDrawableMultisample4X;
    [self setupVertices];
    [self setupGL];
}

...

#pragma mark - GLKViewDelegate

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
    glClearColor(_curRed, 0.5, 0.5, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);

    [self.effect prepareToDraw];

    glBindVertexArrayOES(_vertexArray);
    glDrawElements(GL_TRIANGLES, sizeof(Indices)/sizeof(Indices[0]), GL_UNSIGNED_BYTE, 0);
}

...

#pragma mark - OpenGL stuff
- (void)setupGL {

    [EAGLContext setCurrentContext:self.context];
    glEnable(GL_CULL_FACE);

    glGenVertexArraysOES(1, &_vertexArray);
    glBindVertexArrayOES(_vertexArray);
// ----- create new buffer,  work with "vertexBuffer", glBufferData sends data for opengl usage
    glGenBuffers(1, &_vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);

    glGenBuffers(1, &_indexBuffer);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW);

// ----- Setup vertices attributes
    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Position));
    glEnableVertexAttribArray(GLKVertexAttribColor);
    glVertexAttribPointer(GLKVertexAttribColor, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Color));
}

- (void)tearDownGL {

    [EAGLContext setCurrentContext:self.context];

    glDeleteBuffers(1, &_vertexBuffer);
    glDeleteBuffers(1, &_indexBuffer);
    glDeleteVertexArraysOES(1, &_vertexArray);

    self.effect = nil;

}

- (void)setupVertices
{ // test
    int points = 3;
    Vertices = malloc(sizeof(Vertex) * points);
    Vertex v = {{0, 0, 0}, {0, 0, 0, 1}};
    Vertices[0] = v;
    Vertex v1 = {{1, 1, 0}, {0, 1, 0, 1}};
    Vertices[1] = v1;
    Vertex v2 = {{0, 1, 1}, {1, 0, 0, 1}};
    Vertices[2] = v2;
}

@end

Answer 1

改变

glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);

到

glBufferData(GL_ARRAY_BUFFER, sizeof(vertex) * 3, Vertices, GL_STATIC_DRAW);

您的问题是 sizeof(vertices) 对指针的工作方式不同于对分配在堆栈上的数组的工作方式。