如何将此OpenGL指针数学转换为Swift？

Question

我正在学习本教程关于iOS的OpenGL/GLKit的,但试图在Swift中实现它.在我到达这个部分之前一切正常:

- (void)render { 

// 1
self.effect.texture2d0.name = self.textureInfo.name;
self.effect.texture2d0.enabled = YES;

// 2    
[self.effect prepareToDraw];

// 3
glEnableVertexAttribArray(GLKVertexAttribPosition);
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);

//---------------- This is where things break down...
long offset = (long)&_quad;        
glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset + offsetof(TexturedVertex, geometryVertex)));
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset + offsetof(TexturedVertex, textureVertex)));

// 5    
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

}

@end

我有一个房产 self.quad像这样的Swift结构:

struct TexturedVertex {
let geometryVertex: CGPoint
let textureVertex: CGPoint
}

struct TexturedQuad {

let bottomLeft: TexturedVertex
let bottomRight: TexturedVertex
let topLeft: TexturedVertex
let topRight: TexturedVertex
}

这是一个相当简单的结构,但我不知道如何将它传递给最后一个参数glVertexAttribPointer.任何帮助都会很棒!

Answer 1

在Swift中,您可以使用泛型结构UnsafePointer来执行指针算术和转换.Swift没有offsetof,但你可以通过直接UnsafePointer使用geometryVertex和textureVertex元素来干净地解决这个问题.

以下代码在iOS操场中编译.我没有测试过它,但我认为它会起作用:

import OpenGLES
import GLKit

struct TexturedVertex {
    var geometryVertex = GLKVector2()
    var textureVertex = GLKVector2()
}

struct TexturedQuad {
    var bl = TexturedVertex()
    var br = TexturedVertex()
    var tl = TexturedVertex()
    var tr = TexturedVertex()
    init() { }
}

var _quad = TexturedQuad()
withUnsafePointer(&_quad.bl.geometryVertex) { (pointer) -> Void in
    glVertexAttribPointer(GLuint(GLKVertexAttrib.Position.rawValue),
        2, GLenum(GL_FLOAT), GLboolean(GL_FALSE),
        GLsizei(sizeof(TexturedVertex)), pointer)
}
withUnsafePointer(&_quad.bl.textureVertex) { (pointer) -> Void in
    glVertexAttribPointer(GLuint(GLKVertexAttrib.TexCoord0.rawValue),
        2, GLenum(GL_FLOAT), GLboolean(GL_FALSE),
        GLsizei(sizeof(TexturedVertex)), pointer)
}

顺便说一下,使用CGPoint你在问题中的方式是危险的,因为CGFloat根据你的目标(32位或64位)改变大小,但GL_FLOAT总是意味着32位.您正在关注的教程是在64位iOS出现之前编写的.