iOS上的OpenGL ES 2.0对象选取

Question

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.

Answer 1

这是颜色拣选的工作原型,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).

这里还有一些属性:

@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(或者你的3d场景中的一些物体),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屏幕水龙头(在这种情况下为@point)转换为棋子实例.

每件作品都有其独特的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.然后有了密封,您可以通过以下方式轻松找到您的碎片哈希表或数组:

-(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];
}

这里还有我使用的glkview设置/清理功能.

- (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];
}

希望这有帮助,并可能永远关闭"挑选问题":)

Answer 2

以下是基于上述解决方案的方法,使用深度缓冲区进行3D拾取,使用GLKVector3签名来检索密封:

• 我的所有物品都有封印
• 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(您想要的顶点或片段)

添加一个挑选布尔值,告诉您是否进行了选择传球

uniform bool picking;

和GLKVector3

uniform vec3 color;

如果激活布尔选择,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;
}

并且视图控制器代码从触摸位置获取像素并从所选颜色中获取所选密封:

-(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.