7.8: Collision Detection

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\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

        # check if the worm has hit itself or the edge
        if wormCoords[HEAD]['x'] == -1 or wormCoords[HEAD]['x'] == CELLWIDTH or wormCoords[HEAD]['y'] == -1 or wormCoords[HEAD]['y'] == CELLHEIGHT:
            return # game over
        for wormBody in wormCoords[1:]:
            if wormBody['x'] == wormCoords[HEAD]['x'] and wormBody['y'] == wormCoords[HEAD]['y']:
                return # game over

The worm has crashed when the head has moved off the edge of the grid or when the head moves onto a cell that is already occupied by another body segment.

We can check if the head has moved off the edge of the grid by seeing if either the X coordinate of the head (which is stored in wormCoords[HEAD]['x']) is -1 (which is past the left edge of the grid) or equal to CELLWIDTH (which is past the right edge, since the rightmost X cell coordinate is one less than CELLWIDTH).

The head has also moved off the grid if the Y coordinate of the head (which is stored in wormCoords[HEAD]['y']) is either -1 (which is past the top edge) or CELLHEIGHT (which is past the bottom edge).

All we have to do to end the current game is to return out of runGame(). When runGame() returns to the function call in main(), the next line after the runGame() call (line 46) is the call to showGameOverScreen() which makes the large "Game Over" text appear. This is why we have the return statement on line 3 [79].

Line 4 [80] loops through every body segment in wormCoords after the head (which is at index 0. This is why the for loop iterates over wormCoords[1:] instead of just wormCoords). If both the 'x' and 'y' values of the body segment are the same as the 'x' and 'y' of the head, then we also end the game by returning out of the runGame() function.