GPUImageContext类，提供OpenGL ES基本环境，我们一般不会用到，所以讲的很简单。
属性
@property(readonly, nonatomic) dispatch_queue_t contextQueue
说明：创建一个context线程
描述：_contextQueue = dispatch_queue_create("com.sunsetlakesoftware.GPUImage.openGLESContextQueue", NULL);
@property(readwrite, retain, nonatomic) GLProgram *currentShaderProgram
说明：当前着色器program
@property(readonly, retain, nonatomic) EAGLContext *context
说明：opengl es绘制环境，管理上下文
方法
+ (void *)contextKey
说明：设置当前context的线程标识符，全局静态变量。
+ (GPUImageContext *)sharedImageProcessingContext
说明：创建一个全局的GPUImageContext对象的单例。
+ (dispatch_queue_t)sharedContextQueue
说明：创建一个context queue单例
+ (GPUImageFramebufferCache *)sharedFramebufferCache
说明：创建一个GPUFramebufferCache单例
- (void)useAsCurrentContext
说明：使用当前context
+ (void)setActiveShaderProgram:(GLProgram *)shaderProgram;
- (void)setContextShaderProgram:(GLProgram *)shaderProgram;
+ (GLint)maximumTextureSizeForThisDevice;
+ (GLint)maximumTextureUnitsForThisDevice;
+ (GLint)maximumVaryingVectorsForThisDevice;
+ (BOOL)deviceSupportsOpenGLESExtension:(NSString *)extension;
+ (BOOL)deviceSupportsRedTextures;
+ (BOOL)deviceSupportsFramebufferReads;
+ (CGSize)sizeThatFitsWithinATextureForSize:(CGSize)inputSize;
- (void)presentBufferForDisplay;
- (GLProgram *)programForVertexShaderString:(NSString *)vertexShaderString fragmentShaderString:(NSString *)fragmentShaderString;
- (void)useSharegroup:(EAGLSharegroup *)sharegroup;
+ (BOOL)supportsFastTextureUpload;
完整代码
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#import "GLProgram.h"#import "GPUImageFramebuffer.h"#import "GPUImageFramebufferCache.h"#define GPUImageRotationSwapsWidthAndHeight(rotation) ((rotation) == kGPUImageRotateLeft || (rotation) == kGPUImageRotateRight || (rotation) == kGPUImageRotateRightFlipVertical || (rotation) == kGPUImageRotateRightFlipHorizontal)typedef enum { kGPUImageNoRotation, kGPUImageRotateLeft, kGPUImageRotateRight, kGPUImageFlipVertical, kGPUImageFlipHorizonal, kGPUImageRotateRightFlipVertical, kGPUImageRotateRightFlipHorizontal, kGPUImageRotate180 } GPUImageRotationMode;@interface GPUImageContext : NSObject@property(readonly, nonatomic) dispatch_queue_t contextQueue;@property(readwrite, retain, nonatomic) GLProgram *currentShaderProgram;@property(readonly, retain, nonatomic) EAGLContext *context;@property(readonly) CVOpenGLESTextureCacheRef coreVideoTextureCache;@property(readonly) GPUImageFramebufferCache *framebufferCache;+ (void *)contextKey;+ (GPUImageContext *)sharedImageProcessingContext;+ (dispatch_queue_t)sharedContextQueue;+ (GPUImageFramebufferCache *)sharedFramebufferCache;+ (void)useImageProcessingContext;- (void)useAsCurrentContext;+ (void)setActiveShaderProgram:(GLProgram *)shaderProgram;- (void)setContextShaderProgram:(GLProgram *)shaderProgram;+ (GLint)maximumTextureSizeForThisDevice;+ (GLint)maximumTextureUnitsForThisDevice;+ (GLint)maximumVaryingVectorsForThisDevice;+ (BOOL)deviceSupportsOpenGLESExtension:(NSString *)extension;+ (BOOL)deviceSupportsRedTextures;+ (BOOL)deviceSupportsFramebufferReads;+ (CGSize)sizeThatFitsWithinATextureForSize:(CGSize)inputSize;- (void)presentBufferForDisplay;- (GLProgram *)programForVertexShaderString:(NSString *)vertexShaderString fragmentShaderString:(NSString *)fragmentShaderString;- (void)useSharegroup:(EAGLSharegroup *)sharegroup;// Manage fast texture upload+ (BOOL)supportsFastTextureUpload;@end@protocol GPUImageInput <NSObject>- (void)newFrameReadyAtTime:(CMTime)frameTime atIndex:(NSInteger)textureIndex;- (void)setInputFramebuffer:(GPUImageFramebuffer *)newInputFramebuffer atIndex:(NSInteger)textureIndex;- (NSInteger)nextAvailableTextureIndex;- (void)setInputSize:(CGSize)newSize atIndex:(NSInteger)textureIndex;- (void)setInputRotation:(GPUImageRotationMode)newInputRotation atIndex:(NSInteger)textureIndex;- (CGSize)maximumOutputSize;- (void)endProcessing;- (BOOL)shouldIgnoreUpdatesToThisTarget;- (BOOL)enabled;- (BOOL)wantsMonochromeInput;- (void)setCurrentlyReceivingMonochromeInput:(BOOL)newValue;@endView Code
#import "GPUImageContext.h"#import <OpenGLES/EAGLDrawable.h>#import <AVFoundation/AVFoundation.h>#define MAXSHADERPROGRAMSALLOWEDINCACHE 40@interface GPUImageContext(){ NSMutableDictionary *shaderProgramCache; NSMutableArray *shaderProgramUsageHistory; EAGLSharegroup *_sharegroup;}@end@implementation GPUImageContext@synthesize context = _context;@synthesize currentShaderProgram = _currentShaderProgram;@synthesize contextQueue = _contextQueue;@synthesize coreVideoTextureCache = _coreVideoTextureCache;@synthesize framebufferCache = _framebufferCache;static void *openGLESContextQueueKey;- (id)init;{ if (!(self = [super init])) { return nil; } openGLESContextQueueKey = &openGLESContextQueueKey; _contextQueue = dispatch_queue_create("com.sunsetlakesoftware.GPUImage.openGLESContextQueue", NULL); #if OS_OBJECT_USE_OBJC dispatch_queue_set_specific(_contextQueue, openGLESContextQueueKey, (__bridge void *)self, NULL);#endif shaderProgramCache = [[NSMutableDictionary alloc] init]; shaderProgramUsageHistory = [[NSMutableArray alloc] init]; return self;}+ (void *)contextKey { return openGLESContextQueueKey;}// Based on Colin Wheeler's example here: http://cocoasamurai.blogspot.com/2011/04/singletons-your-doing-them-wrong.html+ (GPUImageContext *)sharedImageProcessingContext;{ static dispatch_once_t pred; static GPUImageContext *sharedImageProcessingContext = nil; dispatch_once(&pred, ^{ sharedImageProcessingContext = [[[self class] alloc] init]; }); return sharedImageProcessingContext;}+ (dispatch_queue_t)sharedContextQueue;{ return [[self sharedImageProcessingContext] contextQueue];}+ (GPUImageFramebufferCache *)sharedFramebufferCache;{ return [[self sharedImageProcessingContext] framebufferCache];}+ (void)useImageProcessingContext;{ [[GPUImageContext sharedImageProcessingContext] useAsCurrentContext];}- (void)useAsCurrentContext;{ EAGLContext *imageProcessingContext = [self context]; if ([EAGLContext currentContext] != imageProcessingContext) { [EAGLContext setCurrentContext:imageProcessingContext]; }}+ (void)setActiveShaderProgram:(GLProgram *)shaderProgram;{ GPUImageContext *sharedContext = [GPUImageContext sharedImageProcessingContext]; [sharedContext setContextShaderProgram:shaderProgram];}- (void)setContextShaderProgram:(GLProgram *)shaderProgram;{ EAGLContext *imageProcessingContext = [self context]; if ([EAGLContext currentContext] != imageProcessingContext) { [EAGLContext setCurrentContext:imageProcessingContext]; } if (self.currentShaderProgram != shaderProgram) { self.currentShaderProgram = shaderProgram; [shaderProgram use]; }}+ (GLint)maximumTextureSizeForThisDevice;{ static dispatch_once_t pred; static GLint maxTextureSize = 0; dispatch_once(&pred, ^{ [self useImageProcessingContext]; glGetIntegerv(GL_MAX_TEXTURE_SIZE, &maxTextureSize); }); return maxTextureSize;}+ (GLint)maximumTextureUnitsForThisDevice;{ static dispatch_once_t pred; static GLint maxTextureUnits = 0; dispatch_once(&pred, ^{ [self useImageProcessingContext]; glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &maxTextureUnits); }); return maxTextureUnits;}+ (GLint)maximumVaryingVectorsForThisDevice;{ static dispatch_once_t pred; static GLint maxVaryingVectors = 0; dispatch_once(&pred, ^{ [self useImageProcessingContext]; glGetIntegerv(GL_MAX_VARYING_VECTORS, &maxVaryingVectors); }); return maxVaryingVectors;}+ (BOOL)deviceSupportsOpenGLESExtension:(NSString *)extension;{ static dispatch_once_t pred; static NSArray *extensionNames = nil; // Cache extensions for later quick reference, since this won't change for a given device dispatch_once(&pred, ^{ [GPUImageContext useImageProcessingContext]; NSString *extensionsString = [NSString stringWithCString:(const char *)glGetString(GL_EXTENSIONS) encoding:NSASCIIStringEncoding]; extensionNames = [extensionsString componentsSeparatedByString:@" "]; }); return [extensionNames containsObject:extension];}// http://www.khronos.org/registry/gles/extensions/EXT/EXT_texture_rg.txt+ (BOOL)deviceSupportsRedTextures;{ static dispatch_once_t pred; static BOOL supportsRedTextures = NO; dispatch_once(&pred, ^{ supportsRedTextures = [GPUImageContext deviceSupportsOpenGLESExtension:@"GL_EXT_texture_rg"]; }); return supportsRedTextures;}+ (BOOL)deviceSupportsFramebufferReads;{ static dispatch_once_t pred; static BOOL supportsFramebufferReads = NO; dispatch_once(&pred, ^{ supportsFramebufferReads = [GPUImageContext deviceSupportsOpenGLESExtension:@"GL_EXT_shader_framebuffer_fetch"]; }); return supportsFramebufferReads;}+ (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;}- (void)presentBufferForDisplay;{ [self.context presentRenderbuffer:GL_RENDERBUFFER];}- (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;}- (void)useSharegroup:(EAGLSharegroup *)sharegroup;{ NSAssert(_context == nil, @"Unable to use a share group when the context has already been created. Call this method before you use the context for the first time."); _sharegroup = sharegroup;}- (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;}#pragma mark -#pragma mark Manage fast texture upload+ (BOOL)supportsFastTextureUpload;{#if TARGET_IPHONE_SIMULATOR return NO;#else #pragma clang diagnostic push#pragma clang diagnostic ignored "-Wtautological-pointer-compare" return (CVOpenGLESTextureCacheCreate != NULL);#pragma clang diagnostic pop#endif}#pragma mark -#pragma mark Accessors- (EAGLContext *)context;{ if (_context == nil) { _context = [self createContext]; [EAGLContext setCurrentContext:_context]; // Set up a few global settings for the image processing pipeline glDisable(GL_DEPTH_TEST); } return _context;}- (CVOpenGLESTextureCacheRef)coreVideoTextureCache;{ if (_coreVideoTextureCache == NULL) {#if defined(__IPHONE_6_0) CVReturn err = CVOpenGLESTextureCacheCreate(kCFAllocatorDefault, NULL, [self context], NULL, &_coreVideoTextureCache);#else CVReturn err = CVOpenGLESTextureCacheCreate(kCFAllocatorDefault, NULL, (__bridge void *)[self context], NULL, &_coreVideoTextureCache);#endif if (err) { NSAssert(NO, @"Error at CVOpenGLESTextureCacheCreate %d", err); } } return _coreVideoTextureCache;}- (GPUImageFramebufferCache *)framebufferCache;{ if (_framebufferCache == nil) { _framebufferCache = [[GPUImageFramebufferCache alloc] init]; } return _framebufferCache;}@endView Code
原标题：GPUImage API文档之GPUImageContext类
关键词：
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