GPUImageContext类，提供OpenGL ES基本上下文，GPUImage相关处理线程，GLProgram缓存、帧缓存。由于是上下文对象，因此该模块提供的更多是存取、设置相关的方法。
- 属性列表
// GPUImage处理OpenGL绘制的相关队列，串行队列
@property(readonly, nonatomic) dispatch_queue_t contextQueue;
// 当前使用的着色器程序
@property(readwrite, retain, nonatomic) GLProgram *currentShaderProgram;
// OpenGLES上下文对象
@property(readonly, retain, nonatomic) EAGLContext *context;
// CoreVideo中的纹理缓存
@property(readonly) CVOpenGLESTextureCacheRef coreVideoTextureCache;
// 帧缓存
@property(readonly) GPUImageFramebufferCache *framebufferCache;
- 初始化过程。在初始化的过程中通过dispatch_queue_set_specific设置队列标识
- (id)init;
{
if (!(self = [super init]))
{
return nil;
}
// 创建OpenGL渲染队列
openGLESContextQueueKey = &openGLESContextQueueKey;
_contextQueue = dispatch_queue_create("com.sunsetlakesoftware.GPUImage.openGLESContextQueue", GPUImageDefaultQueueAttribute());
#if OS_OBJECT_USE_OBJC
// 设置队列标识
dispatch_queue_set_specific(_contextQueue, openGLESContextQueueKey, (__bridge void *)self, NULL);
#endif
// 初始化着色器缓存相关数组
shaderProgramCache = [[NSMutableDictionary alloc] init];
shaderProgramUsageHistory = [[NSMutableArray alloc] init];
return self;
}
- 方法列表
// 获取队列标识
+ (void *)contextKey;
// 单例对象
+ (GPUImageContext *)sharedImageProcessingContext;
// 获取处理队列
+ (dispatch_queue_t)sharedContextQueue;
// 帧缓存
+ (GPUImageFramebufferCache *)sharedFramebufferCache;
// 设置当前上下文
+ (void)useImageProcessingContext;
- (void)useAsCurrentContext;
// 设置当前的GL程序
+ (void)setActiveShaderProgram:(GLProgram *)shaderProgram;
- (void)setContextShaderProgram:(GLProgram *)shaderProgram;
// 获取设备OpenGLES相关特性的支持情况
+ (GLint)maximumTextureSizeForThisDevice;
+ (GLint)maximumTextureUnitsForThisDevice;
+ (GLint)maximumVaryingVectorsForThisDevice;
+ (BOOL)deviceSupportsOpenGLESExtension:(NSString *)extension;
+ (BOOL)deviceSupportsRedTextures;
+ (BOOL)deviceSupportsFramebufferReads;
// 纹理大小调整，保证纹理不超过OpenGLES支持最大的尺寸
+ (CGSize)sizeThatFitsWithinATextureForSize:(CGSize)inputSize;
// 将渲染缓存呈现在设备上
- (void)presentBufferForDisplay;
// 创建GLProgram，首先在缓存中查找，如果没有则创建
- (GLProgram *)programForVertexShaderString:(NSString *)vertexShaderString fragmentShaderString:(NSString *)fragmentShaderString;
// 创建Sharegroup
- (void)useSharegroup:(EAGLSharegroup *)sharegroup;
// Manage fast texture upload
+ (BOOL)supportsFastTextureUpload;
由于GPUImageContext相当于一个上下文对象，主要是管理其它的对象，因此该类没有太多复杂的业务，这里主要看一下几个方法：
- 调整纹理大小，保证纹理不超过OpenGLES支持最大的尺寸：
+ (CGSize)sizeThatFitsWithinATextureForSize:(CGSize)inputSize;
{
GLint maxTextureSize = [self maximumTextureSizeForThisDevice];
if ( (inputSize.width < maxTextureSize) && (inputSize.height < maxTextureSize) )
{
return inputSize;
}
CGSize adjustedSize;
if (inputSize.width > inputSize.height)
{
adjustedSize.width = (CGFloat)maxTextureSize;
adjustedSize.height = ((CGFloat)maxTextureSize / inputSize.width) * inputSize.height;
}
else
{
adjustedSize.height = (CGFloat)maxTextureSize;
adjustedSize.width = ((CGFloat)maxTextureSize / inputSize.height) * inputSize.width;
}
return adjustedSize;
}
- 获取OpenGLES支持的最大纹理尺寸
+ (GLint)maximumTextureSizeForThisDevice;
{
static dispatch_once_t pred;
static GLint maxTextureSize = 0;
dispatch_once(&pred, ^{
[self useImageProcessingContext];
glGetIntegerv(GL_MAX_TEXTURE_SIZE, &maxTextureSize);
});
return maxTextureSize;
}
- 创建GLProgram，首先在缓存中查找，如果没有则创建
- (GLProgram *)programForVertexShaderString:(NSString *)vertexShaderString fragmentShaderString:(NSString *)fragmentShaderString;
{
NSString *lookupKeyForShaderProgram = [NSString stringWithFormat:@"V: %@ - F: %@", vertexShaderString, fragmentShaderString];
GLProgram *programFromCache = [shaderProgramCache objectForKey:lookupKeyForShaderProgram];
if (programFromCache == nil)
{
programFromCache = [[GLProgram alloc] initWithVertexShaderString:vertexShaderString fragmentShaderString:fragmentShaderString];
[shaderProgramCache setObject:programFromCache forKey:lookupKeyForShaderProgram];
// [shaderProgramUsageHistory addObject:lookupKeyForShaderProgram];
// if ([shaderProgramUsageHistory count] >= MAXSHADERPROGRAMSALLOWEDINCACHE)
// {
// for (NSUInteger currentShaderProgramRemovedFromCache = 0; currentShaderProgramRemovedFromCache < 10; currentShaderProgramRemovedFromCache++)
// {
// NSString *shaderProgramToRemoveFromCache = [shaderProgramUsageHistory objectAtIndex:0];
// [shaderProgramUsageHistory removeObjectAtIndex:0];
// [shaderProgramCache removeObjectForKey:shaderProgramToRemoveFromCache];
// }
// }
}
return programFromCache;
}
- 创建EAGLContext上下文对象，使用的是kEAGLRenderingAPIOpenGLES2的API也就是OpenGL ES 2.0
- (EAGLContext *)createContext;
{
EAGLContext *context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2 sharegroup:_sharegroup];
NSAssert(context != nil, @"Unable to create an OpenGL ES 2.0 context. The GPUImage framework requires OpenGL ES 2.0 support to work.");
return context;
}
- 设置当前的上下文对象，以及当前的着色器程序
- (void)setContextShaderProgram:(GLProgram *)shaderProgram;
{
EAGLContext *imageProcessingContext = [self context];
if ([EAGLContext currentContext] != imageProcessingContext)
{
[EAGLContext setCurrentContext:imageProcessingContext];
}
if (self.currentShaderProgram != shaderProgram)
{
self.currentShaderProgram = shaderProgram;
[shaderProgram use];
}
}
总结
GLProgram 与着色器程序创建息息相关，其中包括创建、编译、链接、使用等过程。
GPUImageContext 是GPUImage的上下文对象，管理着OpenGLES上下文对象，管理着GL程序，管理着帧缓存等GPUImage中的基本组件。