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。
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：
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。