只有一个单色的三角形，总归是不好看，下面就往上面粘贴一个图片。纹理贴图会引入映射、UV坐标等概念。
#import "GameViewController.h"
#import <OpenGLES/ES2/glext.h>
//将顶点坐标和UV纹理坐标放入同一个数据中
typedef struct {
GLKVector3 positionCoords;
GLKVector2 textureCoords;
} VertexType;
//三角形顶点数据
static const VertexType vertices[] = {
{{-0.5f, -0.5f, 0.0f}, {0.0f, 0.0f}},
{{0.5f, -0.5f, 0.0f}, {1.0f, 0.0f}},
{{-0.5f, 0.5f, 0.0f}, {0.0f, 1.0f}}
};
@interface GameViewController () {
GLuint vertexBufferID;
}
//用于设置通用的OpenGL ES环境
@property (strong, nonatomic) GLKBaseEffect *baseEffect;
//OpenGL ES上下文
@property (strong, nonatomic) EAGLContext *context;
@end
@implementation GameViewController
- (void)viewDidLoad
{
[super viewDidLoad];
//使用支持OpenGL ES2的上下文
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.drawableDepthFormat = GLKViewDrawableDepthFormat24;
[EAGLContext setCurrentContext:self.context];
self.baseEffect = [[GLKBaseEffect alloc] init];
//启用元素的默认颜色
// self.baseEffect.useConstantColor = GL_TRUE;
//设置默认颜色
// self.baseEffect.constantColor = GLKVector4Make(0.0f, 1.0f, 1.0f, 1.0f);
//生成纹理，由于UIKit的坐标系Y轴与OpenGL ES的Y轴刚好上下颠倒，因此如果图片不加任何处理的话，在贴图后将是颠倒显示
CGImageRef imageRef = [UIImage imageNamed:@"1.jpg"].CGImage;
GLKTextureInfo *textureInfo = [GLKTextureLoader textureWithCGImage:imageRef options:NULL error:nil];
self.baseEffect.texture2d0.name = textureInfo.name;
self.baseEffect.texture2d0.target = textureInfo.target;
//设置背景色
glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
//1. 生成缓存ID
glGenBuffers(1, &vertexBufferID);
//2.
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferID);
//3.
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
}
- (BOOL)prefersStatusBarHidden {
return YES;
}
#pragma mark - GLKView and GLKViewController delegate methods
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
[self.baseEffect prepareToDraw];
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//4. 顶点坐标（x, y, z）
glEnableVertexAttribArray(GLKVertexAttribPosition);
//5. 类型，成员个数，类型，归一化，间隔，偏移
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(VertexType), NULL + offsetof(VertexType, positionCoords));
//4.1 纹理坐标(u, v)
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
//5.1
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(VertexType), NULL + offsetof(VertexType, textureCoords));
//6. 绘制
glDrawArrays(GL_TRIANGLES, 0, 3);
}
- (void)dealloc
{
if ([EAGLContext currentContext] == self.context) {
[EAGLContext setCurrentContext:nil];
}
glDeleteBuffers(1, &vertexBufferID);
vertexBufferID = 0;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
if ([self isViewLoaded] && ([[self view] window] == nil)) {
self.view = nil;
if ([EAGLContext currentContext] == self.context) {
[EAGLContext setCurrentContext:nil];
}
self.context = nil;
glDeleteBuffers(1, &vertexBufferID);
vertexBufferID = 0;
}
}
@end
UIImage获取的CGImageRefY坐标方向与OpenGL ES的Y坐标相反，因此看到的图片是反的。
难点是glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(VertexType), NULL + offsetof(VertexType, positionCoords));的参数含义：
- 顶点属性类型
- 该类型每个顶点所含数据个数
- 数据类型
- 是否归一化
- 每个顶点数组间的间隔（即每个顶点的数据所占空间大小）
- 该类型的数据起始位置相对于起点的偏移量
offsetof用来获取结构体的成员positionCoords在整个结构体VertexType中的偏移量。
