Checking if a point is inside a rotating view

Discussion in 'Programming' started by Ziphold, Nov 11, 2017.

  1. Ziphold

    Ziphold Member

    Jun 22, 2016
    Hello again!
    I'm currently implementing culling in my game and everything works fine until I start rotating the view.
    This is the simple portion of code that controls it.
    lastPointInView = point_in_rectangle(lastPointX,lastPointY,view_xview,view_yview,view_xview+view_wview,view_yview+view_hview);    
    if !lastPointInView {
        lastPointIndex ++;
    Now, because the view is rotating, that wouldn't always work because view_wview and view_hview are always the same, independent of the room view. So sometimes, the code would take effect even when the point is in view, and sometimes it wouldn't when the point is out of it. (Which is opposite of what I want)

    I would be thankful if anyone posted their idea of how I could solve this.
    In advance, thank you.
  2. jaydee

    jaydee Member

    Dec 27, 2016
    Apply the rotation transform to the lastPoint vector before doing your point_in_rectangle test.

    // Assuming here that the origin of your rotation is the centre of the view:
    var OriginX = view_xview + view_wview / 2;
    var OriginY = view_yview + view_hview / 2;
    // Find position of LastPoint relative to Origin
    var OffsetX = lastPointX - OriginX;
    var OffsetY = lastPointY - OriginY;
    // Apply rotation
    OffsetX *= cosd(view_angle);
    OffsetY *= sind(view_angle);
    // Transform back into world coordinates
    lastPointX = OriginX + OffsetX;
    lastPointY = OriginY + OffsetY;
    Could be condensed or made into a script, but I wanted each step to be clear. Might need to double check the math, but I think it should all be right.

    *Note* Whether this would work or not depends on what exactly lastPoint is! In the case this doesn't work, there are two things you should try:

    1) In my code, replace view_angle with -view_angle.
    2) Instead of applying the rotation transform to your x and y boundaries instead of lastPoint.

    If after all 3 this isn't working, I'll need more information to help you.
    Last edited: Nov 11, 2017
  3. NightFrost

    NightFrost Member

    Jun 24, 2016
    Shouldn't the rotation be
    OffsetX = OffsetX * dcos(view_angle) - OffsetY * dsin(view_angle);
    OffsetY = OffsetY * dcos(view_angle) + OffsetX * dsin(view_angle);
  4. Wraithious

    Wraithious Member

    Jun 24, 2016
    You could use point_in_circle(,,,,,,) with the radius being 1/2 the width of the narrowest side of the view, OR if you need the whole rectangle to be considered an easy way to do it would be to have an object with a blank sprite the size of your view, with the not precise box checked in the sprite editor, mimic your view's x,y, origin and image angle and just check for a collision

    a third option is to use point_in_triangle(,,,,,,,) twice making sure each triangle is of the right triangle type to form a rectangle, and then use length_direction(,,,) and point_direction(,,,) to update the points of the triangles to match the view's rotation.
    Last edited: Nov 12, 2017
  5. Ziphold

    Ziphold Member

    Jun 22, 2016
    Sorry for the late answer, guys. Anyways, I used each method and found out there is more to it than what I expected. So instead of deactivating points outside the view, I constantly deactivate 20th point in the list (which is always outside the view).
    I'm very thankful for the answers, however!
    Wraithious likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice