How to limit lines to across a set area?

  • I'm making a puzzle game in which the player creates lines across a set area. They do this by clicking two points within the area, and the game plots the lines across the points.

    My problem is how to prevent the lines from extending past the area edges. Here is a capx file which shows the problem (the area that should contain the lines is the dark area in the middle):

    dropbox.com/s/gbm6ie2q0ib3s5a/bounded_lines.capx

    FWIW, the solutions I've considered / tried are:

    1) Overlay a background image that is transparent over the drawing area, but obscures the rest of the screen. I plan to add video backgrounds later, so this isn't suitable here.

    2) Set invisible sprites around the area edges and check for where the line collides with them

    From my forum searches, it seems that checking for collision points on two sprites is difficult. The best solution I could come up with was to have invisible single pixel sprites that run along the edges of the set area and check for collisions where the lines exit the area, then place sprites on either side and draw new, shorter lines between them using distance joints. This seems workable, but really inefficient.

    3) Use the initial x and y coordinates of the specified points, and the x and y axes of the area to mathemagically calculate the exit coordinates of the lines and draw new lines between the points as above. This seems to be best solution I could come up with, but it's way beyond my feeble math ability.

    This is an important point for my game's presentation, so any help would be much appreciated!

  • I would use a mask. Create a new layer, set Force own texture=yes in layer properties. Put black rectangular sprites around the drawing area, set Destination Out blend mode for them. Spawn the line on this layer and move it to the bottom of the layer (masking sprites should be above the line).

    The mask will only hide parts of the line which are outside the drawing area and will not affect other layers.

    There is a "Blend modes" template in Construct 2, you can check it out.

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  • That sounds PERFECT! (I forgot that there will be other objects scrolling out of the game area, too.)

    Thanks very much!!

  • UPDATE: Worked like a CHARM! Thanks again!!

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