我正在使用 OpenGL ES 渲染一些特殊效果，我不想向用户展示，我只想将结果保存为 UIImage，有人可以帮我吗？
这是我正在使用的代码，我可以获得包含我使用的红色透明颜色的图像，但没有显示几何图形。
#import "RendererGL.h"
#import <GLKit/GLKit.h>
#import <UIKit/UIKit.h>
#import <OpenGLES/EAGL.h>
#import <OpenGLES/EAGLDrawable.h>
#import <OpenGLES/ES2/glext.h>
#import <QuartzCore/QuartzCore.h>
static NSInteger WIDTH_IN_PIXEL = 400;
static NSInteger HEIGHT_IN_PIXEL = 300;
typedef struct {
GLKVector3 positionCoords;
}
SceneVertex;
static const SceneVertex vertices[] =
{
{{-0.5f, -0.5f, 0.0}}, // lower left corner
{{ 0.5f, -0.5f, 0.0}}, // lower right corner
{{-0.5f, 0.5f, 0.0}} // upper left corner
};
@implementation RendererGL
{
EAGLContext* _myContext;
GLuint _framebuffer;
GLuint _colorRenderbuffer;
GLuint _depthRenderbuffer;
GLuint _vertexBufferID;
GLKBaseEffect *_baseEffect;
}
- (id) init
{
self = [super init];
if (self)
{
_myContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
[EAGLContext setCurrentContext:_myContext];
[self setupOffscreenBuffer];
[self setUpEffect];
[self renderImage];
[self saveImage]; //this do works, since I get an image, but the image only contains the red color I used to clear
}
return self;
}
-(void)setUpEffect
{
_baseEffect = [[GLKBaseEffect alloc] init];
_baseEffect.useConstantColor = GL_TRUE;
_baseEffect.constantColor = GLKVector4Make(0.0f, 0.0f, 1.0f, 1.0f);
}
//this code is from apples document
-(void)setupOffscreenBuffer
{
glGenFramebuffers(1, &_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
glGenRenderbuffers(1, &_colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA4, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _colorRenderbuffer);
glGenRenderbuffers(1, &_depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, _depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, _depthRenderbuffer);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ;
if(status != GL_FRAMEBUFFER_COMPLETE) {
NSLog(@"failed to make complete framebuffer object %x", status);
}
}
- (void) renderImage
{
GLenum error = GL_NO_ERROR;
glClearColor(1, 0, 0, 1); //red clear color, this can be seen
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
[_baseEffect prepareToDraw];
glGenBuffers(1, &_vertexBufferID);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBufferID);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
error = glGetError();
if (error != GL_NO_ERROR) {
NSLog(@"error happend, error is %d, line %d",error,__LINE__);
}
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition,3,GL_FLOAT, GL_FALSE, sizeof(SceneVertex), NULL);
glDrawArrays(GL_TRIANGLES,0,3);
error = glGetError();
if (error != GL_NO_ERROR) {
NSLog(@"error happend, error is %d, line %d",error,__LINE__);
}
glFinish();
error = glGetError();
if (error != GL_NO_ERROR) {
NSLog(@"error happend, error is %d, line %d",error,__LINE__);
}
}
-(void)saveImage
{
GLenum error = GL_NO_ERROR;
NSInteger x = 0, y = 0;
NSInteger dataLength = WIDTH_IN_PIXEL * HEIGHT_IN_PIXEL * 4;
GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));
glPixelStorei(GL_PACK_ALIGNMENT, 4);
glReadPixels(x, y, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL, GL_RGBA, GL_UNSIGNED_BYTE, data);
NSData *pixelsRead = [NSData dataWithBytes:data length:dataLength];
error = glGetError();
if (error != GL_NO_ERROR) {
NSLog(@"error happend, error is %d, line %d",error,__LINE__);
}
CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGImageRef iref = CGImageCreate(WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL, 8, 32, WIDTH_IN_PIXEL * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast,
ref, NULL, true, kCGRenderingIntentDefault);
UIGraphicsBeginImageContext(CGSizeMake(WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL));
CGContextRef cgcontext = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, WIDTH_IN_PIXEL, HEIGHT_IN_PIXEL), iref);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
NSData *d = UIImageJPEGRepresentation(image, 1);
NSString *documentDirPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
static NSInteger imageNO = 1;
imageNO++;
NSString *savingPath = [documentDirPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%d.jpg",imageNO]];
BOOL succ = [d writeToFile:savingPath atomically:NO]; //is succeeded
UIGraphicsEndImageContext();
free(data);
CFRelease(ref);
CFRelease(colorspace);
CGImageRelease(iref);
}
@end