CODEWITHSUNDEEP
iosobjective-cipadopengl-es-2.0glkit
Martin Berger
Martin Berger

Reputation: 1708

iOS Using GLKMathUnproject to find screen point in world space

How to use GLKMathUnproject to determine location in world space? The user needs to select one of several objects in world space.

In doc it says

GLKVector3 GLKMathUnproject (
   GLKVector3 window,
   GLKMatrix4 model,
   GLKMatrix4 projection,
   int *viewport,
   bool *success
);

but which modelView matrix? I have bunch of models in world. Which model matrix should i use.

My world is 2d, on x,y plane. z is used for camera movement.

If i understood correctly, GLKMathUnproject is used to find a point in model space. How do i know which model? Do i need to determine first the model below the fingers or what?

Upvotes: 0

Views: 1256

Answers (2)

Martin Berger
Martin Berger

Reputation: 1708

- (IBAction)handleTapUnproject:(id)recognizer
{    
    bool success = NO;
    GLfloat realY;

    GLint viewport[4] = {};
    glGetIntegerv(GL_VIEWPORT, viewport);
    NSLog(@"%d, %d, %d, %d", viewport[0], viewport[1], viewport[2], viewport[3]);

    CGPoint touchOrigin = [recognizer locationInView:self.view];
    NSLog(@"tap coordinates: %8.2f, %8.2f", touchOrigin.x, touchOrigin.y);

    realY = viewport[3] - touchOrigin.y;

    GLKMatrix4 modelView = lookAt;

    // near

    GLKVector3 originInWindowNear = GLKVector3Make(touchOrigin.x, realY, 0.0f);

    GLKVector3 result1 = GLKMathUnproject(originInWindowNear, modelView, projectionMatrix, viewport, &success);
    NSAssert(success == YES, @"unproject failure");

    GLKMatrix4 matrix4_1 = GLKMatrix4Translate(GLKMatrix4Identity, result1.x, result1.y, 0.0f);
    _squareUnprojectNear.modelMatrixUsage = GLKMatrix4Multiply(matrix4_1, _squareUnprojectNear.modelMatrixBase);

    GLKVector3 rayOrigin = GLKVector3Make(result1.x, result1.y, result1.z);

    // far

    GLKVector3 originInWindowFar = GLKVector3Make(touchOrigin.x, realY, 1.0f);

    GLKVector3 result2 = GLKMathUnproject(originInWindowFar, modelView, projectionMatrix, viewport, &success);
    NSAssert(success == YES, @"unproject failure");

    GLKMatrix4 matrix4_2 = GLKMatrix4Translate(GLKMatrix4Identity, result2.x, result2.y, 0.0f);

    GLKVector3 rayDirection = GLKVector3Make(result2.x - rayOrigin.x, result2.y - rayOrigin.y, result2.z - rayOrigin.z);
}

So if you want to unproject to world space, you use just your lookAt matrix. And if you want to unproject into model space of a specific object, then you use model * view matrix.

Upvotes: 1

Volodymyr B.
Volodymyr B.

Reputation: 3441

Create simple project, which you be able to create from templates of Xcode, called "OpenGL Game".

model - modelViewMatrix or self.effect.transform.modelviewMatrix

projection - projectionMatrix or self.effect.transform.projectionMatrix

Viewport:

GLint viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);

Your code will be similar to:

GLKVector point = ...;
bool boolValue;    
GLKMathUnproject(point,
                         modelViewMatrix,
                         projectionMatrix, viewport, &boolValue);

Upvotes: 0

Related Questions