iphone - iOS OpenGL ES 2.0: renderizado sin pantalla y guarda el resultado en un UIImage

opengl-es opengl-es-2.0

Question

Estoy usando OpenGL ES para renderizar algunos efectos especiales, no quiero mostrar esto al usuario, solo quiero guardar el resultado como un UIImage, ¿alguien puede ayudarme?

este es el código que estoy usando, puedo obtener una imagen que contenga el color rojo claro que uso, pero no se muestra ningún dibujo de geometría.

#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

Answer 1

No veo una llamada a eglSwapBuffers (). Esto es necesario para comenzar a renderizar el cuadro en PowerVR, incluso cuando se renderiza en un Renderbuffer. Ver el código de ejemplo en:

http://processors.wiki.ti.com/index.php/Render_to_Texture_with_OpenGL_ES

Answer 2

Tuve un problema muy similar: renderizar algunas líneas y obtener UIImage. Usé OpenGL ES 1.1 y multisampling. Eliminé un código adicional que no se refiere a la representación y algunas verificaciones de errores de OpenGL. Puede encontrar el código completo aquí: OSPRendererGL . Además, lo siento por mi método único para todos.

@interface OSPRendererGL
{
    EAGLContext* myContext;
    GLuint framebuffer;
    GLuint colorRenderbuffer;
    GLuint depthRenderbuffer;
    GLuint _vertexArray;
    GLuint _vertexBuffer;
    GLuint resolveFramebuffer;
    GLuint msaaFramebuffer, msaaRenderbuffer, msaaDepthbuffer;

    int width;
    int height;
}

@implementation OSPRendererGL

- (id) init
{
    self = [super init];
    if (self)
    {
        myContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];
        [EAGLContext setCurrentContext:myContext];
        [self setupOpenGL];
        [EAGLContext setCurrentContext:nil];
        width = 256;
        height = 256;
    }
    return self;
}

-(void) setupOpenGL
{
    glGenFramebuffersOES(1, &framebuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);

    glGenRenderbuffersOES(1, &colorRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, width, height);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorRenderbuffer);

    glGenRenderbuffersOES(1, &depthRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
    glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, width, height);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);

    glGenFramebuffersOES(1, &msaaFramebuffer); 
    glGenRenderbuffersOES(1, &msaaRenderbuffer);

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, msaaFramebuffer); 
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, msaaRenderbuffer);   

    glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_RGBA8_OES, width, height); 
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, msaaRenderbuffer); 

    glGenRenderbuffersOES(1, &msaaDepthbuffer);   
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, msaaDepthbuffer); 
    glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_DEPTH_COMPONENT16_OES, width, height); 
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, msaaDepthbuffer);

}

-(UIImage *) renderImageAtZoom:(int)zoom
{
    CGRect b = CGRectMake(0, 0, width, height);
    OSPCoordinateRect r = OSPRectForMapAreaInRect([self mapArea], b);

    double_scale = b.size.width / r.size.x;
    double scale = 1.0/_scale;

    [EAGLContext setCurrentContext:myContext];

    glBindFramebuffer(GL_FRAMEBUFFER_OES, msaaFramebuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, msaaRenderbuffer);

    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrthof(0.0f, 256.0f, 256.0f, 0.0f, 1.0f, -1.0f);
    glMatrixMode(GL_MODELVIEW);

    glPushMatrix();

    glScalef(_scale, _scale, 1);
    glTranslatef(-r.origin.x, -r.origin.y, 0);

    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glEnable(GL_LINE_SMOOTH);
    glEnable(GL_POINT_SMOOTH);
    glEnable(GL_BLEND);

    glClearColor(1, 1, 1, 1);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // rendering here

    glPopMatrix();

    // msaa

    glBindFramebufferOES(GL_READ_FRAMEBUFFER_APPLE, msaaFramebuffer); 
    glBindFramebufferOES(GL_DRAW_FRAMEBUFFER_APPLE, framebuffer);

    glResolveMultisampleFramebufferAPPLE();

    glBindFramebuffer(GL_FRAMEBUFFER_OES, framebuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER, colorRenderbuffer);

    // grabbing image from FBO

    GLint backingWidth, backingHeight;

    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);

    NSInteger x = 0, y = 0;
    NSInteger dataLength = width * height * 4;
    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));

    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);

    CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast,
                                    ref, NULL, true, kCGRenderingIntentDefault);


    UIGraphicsBeginImageContext(CGSizeMake(width, height));
    CGContextRef cgcontext = UIGraphicsGetCurrentContext();
    CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
    CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, width, height), iref);
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    free(data);
    CFRelease(ref);
    CFRelease(colorspace);
    CGImageRelease(iref);

    [EAGLContext setCurrentContext:nil];

    return image;
}