iOS上的OpenGL ES 2.0对象选取

时间:2011-07-21 09:47:12

标签: ios selection opengl-es-2.0 picking

选择在OpenGL ES 2.0(iOS)中绘制的对象的最佳方法是什么?

我在画点。

2 个答案:

答案 0 :(得分:24)

以下是颜色挑选的工作原型,在大多数旧的ipads上测试并且运行良好。这实际上是可以在应用程序商店中找到的名为InCube Chess的项目的一部分。您将看到的主要代码位于从GLKViewController派生的类中,如下所示:

@interface IncubeViewController : GLKViewController

这意味着你有glkview :((GLKView *)self.view)。

以下是一些属性:

@property (strong, nonatomic) EAGLContext *context;
@property (strong, nonatomic) GLKBaseEffect *effect;

不要忘记在* .m文件中合成它们。

@synthesize context = _context;
@synthesize effect = _effect;

这个想法是你的桌子上有棋子(或者3d场景中的某些物体),你需要通过点击屏幕在你的棋子列表中找到一块。也就是说,你需要将你的2d屏幕点击坐标(在这种情况下为@point)转换为棋子实例。

每件作品都有其唯一的ID,我称之为“印章”。您可以将密封从1分配到某个东西。选择功能返回由龙头线圈找到的零件密封。然后你可以用这样的方式找到你的作品哈希表或数组:

-(Piece *)findPieceBySeal:(GLuint)seal
{
        /* !!! Black background in off screen buffer produces 0 seals. This allows
           to quickly filter out taps that did not select anything (will be
           mentioned below) !!! */
        if (seal == 0)
                return nil;
        PieceSeal *sealKey = [[PieceSeal alloc] init:s];
        Piece *p = [sealhash objectForKey:sealKey];
        [sealKey release];
        return p;
}

“sealhash”是一个NSMutableDictionary。

现在这是主要的选择功能。请注意,我的glkview是antialised,你不能使用它的缓冲区进行颜色选择。这意味着您需要创建自己的屏幕外缓冲区,禁用抗锯齿功能,仅用于拣选目的。

- (NSUInteger)findSealByPoint:(CGPoint)point
{
        NSInteger height = ((GLKView *)self.view).drawableHeight;
        NSInteger width = ((GLKView *)self.view).drawableWidth;
        Byte pixelColor[4] = {0,};
        GLuint colorRenderbuffer;
        GLuint framebuffer;

        glGenFramebuffers(1, &framebuffer);
        glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
        glGenRenderbuffers(1, &colorRenderbuffer);
        glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);

        glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8_OES, width, height);
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER, colorRenderbuffer);

        GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
        if (status != GL_FRAMEBUFFER_COMPLETE) {
                NSLog(@"Framebuffer status: %x", (int)status);
                return 0;
        }

        [self render:DM_SELECT];

        CGFloat scale = UIScreen.mainScreen.scale;
        glReadPixels(point.x * scale, (height - (point.y * scale)), 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, pixelColor);

        glDeleteRenderbuffers(1, &colorRenderbuffer);
        glDeleteFramebuffers(1, &framebuffer);

        return pixelColor[0];
}

请注意,功能会考虑显示比例(视网膜或新iPad)。

这是上面函数中使用的render()函数。请注意,出于渲染目的,它清除了具有一些背景颜色的缓冲区,并且为了选择它使其变为黑色,以便您可以轻松地检查是否完全敲击了任何一块。

- (void) render:(DrawMode)mode
{
        if (mode == DM_RENDER)
                glClearColor(backgroundColor.r, backgroundColor.g,
                             backgroundColor.b, 1.0f);
        else
                glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        /* Draw all pieces. */
        for (int i = 0; i < [model->pieces count]; i++) {
                Piece *p = [model->pieces objectAtIndex:i];
                [self drawPiece:p mode:mode];
        }
}

接下来是我们如何绘制这件作品。

- (void) drawPiece:(Piece *)p mode:(DrawMode)mode
{
        PieceType type;

        [self pushMatrix];

        GLKMatrix4 modelViewMatrix = self.effect.transform.modelviewMatrix;

        GLKMatrix4 translateMatrix = GLKMatrix4MakeTranslation(p->drawPos.X,
                                                               p->drawPos.Y,
                                                               p->drawPos.Z);
        modelViewMatrix = GLKMatrix4Multiply(modelViewMatrix, translateMatrix);

        GLKMatrix4 rotateMatrix;
        GLKMatrix4 scaleMatrix;

        if (mode == DM_RENDER) {
                scaleMatrix = GLKMatrix4MakeScale(p->scale.X,
                                                  p->scale.Y, p->scale.Z);
        } else {
                /* !!! Make the piece a bit bigger in off screen buffer for selection
                   purposes so that we always sure that we tapped it correctly by
                   finger.*/
                scaleMatrix = GLKMatrix4MakeScale(p->scale.X + 0.2,
                                                  p->scale.Y + 0.2, p->scale.Z + 0.2);
        }

        modelViewMatrix = GLKMatrix4Multiply(modelViewMatrix, scaleMatrix);

        self.effect.transform.modelviewMatrix = modelViewMatrix;

        type = p->type;

        if (mode == DM_RENDER) {
                /* !!! Use real pieces color and light on for normal drawing !!! */
                GLKVector4 color[pcLast] = {
                        [pcWhite] = whitesColor,
                        [pcBlack] = blacksColor
                };
                self.effect.constantColor = color[p->color];
                self.effect.light0.enabled = GL_TRUE;
        } else {
                /* !!! Use piece seal for color. Important to turn light off !!! */
                self.effect.light0.enabled = GL_FALSE;
                self.effect.constantColor = GLKVector4Make(p->seal / 255.0f,
                                                           0.0f, 0.0f, 0.0f);
        }

        /* Actually normal render the piece using it geometry buffers. */
        [self renderPiece:type];

        [self popMatrix];
}

这是如何使用上面显示的功能。

- (IBAction) tapGesture:(id)sender
{
        if ([(UITapGestureRecognizer *)sender state] == UIGestureRecognizerStateEnded) {
                CGPoint tap = [(UITapGestureRecognizer *)sender locationInView:self.view];
                Piece *p = [self findPieceBySeal:[self findSealByPoint:tap]];

                /* !!! Do something with your selected object !!! */
        }
}

基本上就是这样。您将获得非常精确的拾取算法,该算法比光线跟踪或其他算法要好得多。

这里是push / pop矩阵事的助手。

- (void)pushMatrix
{
        assert(matrixSP < sizeof(matrixStack) / sizeof(GLKMatrix4));
        matrixStack[matrixSP++] = self.effect.transform.modelviewMatrix;
}

- (void)popMatrix
{
        assert(matrixSP > 0);
        self.effect.transform.modelviewMatrix = matrixStack[--matrixSP];
}

这里还有我使用过的glkview setup / cleanup函数。

- (void)viewDidLoad
{
        [super viewDidLoad];
        self.context = [[[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2] autorelease];
        if (!self.context)
                NSLog(@"Failed to create ES context");

        GLKView *view = (GLKView *)self.view;
        view.context = self.context;
        view.drawableDepthFormat = GLKViewDrawableDepthFormat24;

        [self setupGL];
}

- (void)viewDidUnload
{    
        [super viewDidUnload];

        [self tearDownGL];

        if ([EAGLContext currentContext] == self.context)
                [EAGLContext setCurrentContext:nil];
        self.context = nil;
}

- (void)setupGL
{
        [EAGLContext setCurrentContext:self.context];

        self.effect = [[[GLKBaseEffect alloc] init] autorelease];
        if (self.effect) {
                self.effect.useConstantColor = GL_TRUE;
                self.effect.colorMaterialEnabled = GL_TRUE;
                self.effect.light0.enabled = GL_TRUE;
                self.effect.light0.diffuseColor = GLKVector4Make(1.0f, 1.0f, 1.0f, 1.0f);
        }

        /* !!! Draw antialiased geometry !!! */
        ((GLKView *)self.view).drawableMultisample = GLKViewDrawableMultisample4X;
        self.pauseOnWillResignActive = YES;
        self.resumeOnDidBecomeActive = YES;
        self.preferredFramesPerSecond = 30;

        glDisable(GL_DITHER);
        glEnable(GL_CULL_FACE);
        glEnable(GL_DEPTH_TEST);
        glLineWidth(2.0f);

        /* Load pieces geometry */
        [self loadGeometry];
}

- (void)tearDownGL
{
        drawReady = NO;
        [EAGLContext setCurrentContext:self.context];
        [self unloadGeometry];
}

希望这会有所帮助,并可能永远关闭“挑选问题”:)

答案 1 :(得分:5)

基于上述解决方案,我的工作方式是使用深度缓冲区进行3D拾取,使用GLKVector3签名来检索印章:

  • 我的所有物品都有印章
  • 我使用GLKVector3命名颜色从读取像素中检索印章。使用此解决方案,您可以存储255 * 255 * 255 = 16,581,375个对象。

在着色器中(根据需要使用顶点或片段)

添加一个挑选布尔值,告诉您是否进行了选择传递

uniform bool picking;

和GLKVector3

uniform vec3 color;

如果激活布尔选取,那么颜色将是GLKVector3

if(picking)
{
    colorVarying = vec4(color, 1.0);
}

在ViewController中

从封条创建GLKVector3的方法(当我创建一个新的3D对象时):

-(GLKVector3)pack:(uint)seal
{
    GLKVector3 hash;

    float r = seal % 255;
    float g = (seal / 255) % 255;
    float b = (seal / (255 * 255)) % 255;
    hash = GLKVector3Make(r/255, g/255, b/255);

    return hash;
}

视图控制器代码,您可以从触摸位置获取像素并从所选颜色中获取所选的印章:

-(uint)getSealByColor:(GLKVector3)color
{
    color = GLKVector3DivideScalar(color, 255);
    for (MyObject *o in _objects) {
        if(GLKVector3AllEqualToVector3(o.color, color))
        {
            return o.seal;
        }
    }
    return 0;
}

-(void)tap:(UITapGestureRecognizer*)recognizer
{
    CGPoint p = [recognizer locationInView:self.view];
    GLKVector3 i = [self pickingAt:p];
    _sealSelected = [self getSealByColor:i];
}

-(GLKVector3)pickingAt:(CGPoint)position
{
    CGFloat scale = [UIScreen mainScreen].scale;

    GLsizei w = self.view.bounds.size.width * scale;
    GLsizei h = self.view.bounds.size.height * scale;

    GLuint fb;
    GLuint rb;
    GLuint db;

    Byte pixelColor[4] = {0,};

    glGenFramebuffers(1, &fb);
    glBindFramebuffer(GL_FRAMEBUFFER, fb);
    glGenRenderbuffers(1, &rb);
    glBindRenderbuffer(GL_RENDERBUFFER, rb);

    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8_OES, w, h);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rb);

    //here we also create a depth buffer for 3D objects picking
    glGenRenderbuffers(1, &db);
    glBindRenderbuffer(GL_RENDERBUFFER, db);

    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, w, h);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, db);

    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if (status != GL_FRAMEBUFFER_COMPLETE) {
        NSLog(@"Framebuffer status: %x", (int)status);
        return GLKVector3Make(0.0, 0.0, 0.0);
    }

    //we render the scene with our picking boolean activated
    [self render:YES];

    glReadPixels(position.x * scale, (h - (position.y * scale)), 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, pixelColor);

    glDeleteRenderbuffers(1, &db);
    glDeleteRenderbuffers(1, &rb);
    glDeleteFramebuffers(1, &fb);

    return GLKVector3Make(pixelColor[0], pixelColor[1], pixelColor[2]);
}

希望这有助于某人,这就是我如何允许超过255个对象的颜色选择。