Question

我正在关注关于iOS的OpenGL / GLKit this tutorial，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

我有一个属性self.quad，这是一个像这样的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，但是我不知道如何将它传递给glVertexAttribPointer 的最后一个参数。任何帮助都会很棒！

Answer 1

在Swift中，您可以使用泛型struct UnsafePointer来执行指针算法和转换。 Swift没有offsetof，但您可以直接使用UnsafePointer和geometryVertex元素的textureVertex来干净地解决这个问题。

以下代码在iOS游乐场中编译。我还没有测试过它，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在问题中的方式是危险的，因为CGFloat会根据您的目标（32位或64位）更改大小，但是GL_FLOAT总是意味着32位。您关注的教程是在64位iOS发布之前编写的。

如何将此OpenGL指针数学转换为Swift？

1 个答案: