EAGLView创建要点
1 EAGLView的layer为CAEAGLLayer，设置kEAGLDrawablePropertyRetainedBacking和kEAGLDrawablePropertyColorFormat属性
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| - (void)setupLayer{
CAEAGLLayer* layer = (CAEAGLLayer*)self.layer;
layer.opaque = YES;
layer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:@(NO), kEAGLDrawablePropertyRetainedBacking,
kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
}
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2 创建EAGLContext
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| _context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];
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3 加载着着色器程序，获取到着色器变量的索引，此过程，大致可分为：
a获取着色器源文件，创建shader，编译
b创建program，attachShader，link，useProgram
c从program，通过名字获取着色器中变量的索引(后续可以向着色器中传递参数)
这里有一点需要注意，此过程的前提，一定是已经设置了EAGLContext的currentContext
4 每一帧绘制流程
在外面使用CADisplayLink来控制播放帧率，每一帧的绘制流程就是
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| - (void)drawFrame{
[_eaglView setFramebuffer];
[_eaglView draw];
[_eaglView presentFramebuffer];
}
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5 关于frameBuffetObject的创建和释放
前提：context确保设置
流程大致是
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| - (void)createBuffer{
[self checkContext];
glGenRenderbuffers(1, &_colorRenderBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderBuffer);
[_context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer];
glGenFramebuffers(1, &_frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, _frameBuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
GL_RENDERBUFFER, _colorRenderBuffer);
}
- (void)deleteBuffer{
[self checkContext];
glDeleteRenderbuffers(1, &_colorRenderBuffer);
_colorRenderBuffer = 0;
glDeleteFramebuffers(1, &_frameBuffer);
_frameBuffer = 0;
}
- (void)setFramebuffer
{
if ([self checkContext])
{
if (!_frameBuffer){
[self createBuffer];
}
glBindFramebuffer(GL_FRAMEBUFFER, _frameBuffer);
}
}
- (BOOL)presentFramebuffer
{
BOOL success = FALSE;
if ([self checkContext])
{
glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderBuffer);
success = [_context presentRenderbuffer:GL_RENDERBUFFER];
}
return success;
}
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6 关于绘制三角形
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| - (void)draw{
//设置背景颜色为绿色
glClearColor(0, 1.0, 0,1.0);
glClear(GL_COLOR_BUFFER_BIT);
//设置管区域大小
glViewport(0, 0, self.frame.size.width, self.frame.size.height);
GLfloat vertices[] = {
0.0f, 0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f };
//设置着色器中的vPositon
glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, 0, vertices);
//使上一步的设置生效
glEnableVertexAttribArray(_positionSlot);
//绘制三角形
glDrawArrays(GL_TRIANGLES, 0, 3);
}
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