2D screen point from 3D world point, closes #19, thanks @autresphere !

Panorama/PanoramaView.h

@@ -77,13 +77,23 @@
 
 /// Dynamic overlay of latitude and longitude intersection lines for all touches
 @property (nonatomic) BOOL showTouches;
+
+/**
+ * Convert a 3D world-coordinate (specified by a vector distance from origin) to a 2D on-screen coordinate
+ *
+ * @param GLKVector3 coordinate location from origin. Use with CGRectContainsPoint( [[UIScreen mainScreen] bounds], screenPoint )
+ * @return a screen pixel coordinate representation of a 3D world coordinate
+ */
+-(CGPoint)screenLocationFromVector:(GLKVector3)vector;
+
 /**
- * Converts screen coordinate to image pixel coordinate
+ * Converts a 2D on-screen coordinate to a pixel (x,y) of the loaded panorama image
  *
- * @param CGPoint device screen coordinate
- * @return CGPoint image coordinate in pixels, or betwee 0.0 and 1.0 if no image
+ * @param CGPoint screen coordinate
+ * @return CGPoint image coordinate in pixels. If no image, between 0.0 and 1.0
  */
 -(CGPoint) imagePixelAtScreenLocation:(CGPoint)point;
+
 /**
  * Hit-detection for all active touches
  *
@@ -92,6 +102,4 @@
  */
 -(BOOL) touchInRect:(CGRect)rect;
 
-
 @end
-

Panorama/PanoramaView.m

@@ -249,6 +249,24 @@ -(GLKVector3) vectorFromScreenLocation:(CGPoint)screenTouch inAttitude:(GLKMatri
     GLKVector4 vec = GLKMatrix4MultiplyVector4(inverse, screen);
     return GLKVector3Normalize(GLKVector3Make(vec.x, vec.y, vec.z));
 }
+-(CGPoint)screenLocationFromVector:(GLKVector3)vector{
+    GLKMatrix4 matrix = GLKMatrix4Multiply(_projectionMatrix, _attitudeMatrix);
+    GLKVector3 screenVector = GLKMatrix4MultiplyVector3(matrix, vector);
+    return CGPointMake( (screenVector.x/screenVector.z/2.0 + 0.5) * self.frame.size.width,
+                       (0.5-screenVector.y/screenVector.z/2) * self.frame.size.height );
+}
+-(BOOL)computeScreenLocation:(CGPoint*)location fromVector:(GLKVector3)vector inAttitude:(GLKMatrix4)matrix{
+    GLKVector4 screenVector;
+    GLKVector4 vector4;
+    if(location == NULL)
+        return NO;
+    matrix = GLKMatrix4Multiply(_projectionMatrix, matrix);
+    vector4 = GLKVector4Make(vector.x, vector.y, vector.z, 1);
+    screenVector = GLKMatrix4MultiplyVector4(matrix, vector4);
+    location->x = (screenVector.x/screenVector.w/2.0 + 0.5) * self.frame.size.width;
+    location->y = (0.5-screenVector.y/screenVector.w/2) * self.frame.size.height;
+    return (screenVector.z >= 0);
+}
 -(CGPoint) imagePixelFromVector:(GLKVector3)vector{
     CGPoint pxl = CGPointMake((M_PI-atan2f(-vector.z, -vector.x))/(2*M_PI), acosf(vector.y)/M_PI);
     CGPoint tex = [sphere getTextureSize];