.WPLS2 LDY LSX2 \ If LSX2 is non-zero (which indicates the ball line BNE WP1 \ heap is empty), jump to WP1 to reset the line heap \ without redrawing the planet \ Otherwise Y is now 0, so we can use it as a counter to \ loop through the lines in the line heap, redrawing \ each one to remove the planet from the screen, before \ resetting the line heap once we are done .WPL1 CPY LSP \ If Y >= LSP then we have reached the end of the line BCS WP1 \ heap and have finished redrawing the planet (as LSP \ points to the end of the heap), so jump to WP1 to \ reset the line heap, returning from the subroutine \ using a tail call LDA LSY2,Y \ Set A to the y-coordinate of the current heap entry CMP #&FF \ If the y-coordinate is &FF, this indicates that the BEQ WP2 \ next point in the heap denotes the start of a line \ segment, so jump to WP2 to put it into (X1, Y1) STA Y2 \ Set (X2, Y2) to the x- and y-coordinates from the LDA LSX2,Y \ heap STA X2 JSR LOIN \ Draw a line from (X1, Y1) to (X2, Y2) INY \ Increment the loop counter to point to the next point LDA SWAP \ If SWAP is non-zero then we swapped the coordinates BNE WPL1 \ when filling the heap in BLINE, so loop back WPL1 \ for the next point in the heap LDA X2 \ Swap (X1, Y1) and (X2, Y2), so the next segment will STA X1 \ be drawn from the current (X2, Y2) to the next point LDA Y2 \ in the heap STA Y1 JMP WPL1 \ Loop back to WPL1 for the next point in the heap .WP2 INY \ Increment the loop counter to point to the next point LDA LSX2,Y \ Set (X1, Y1) to the x- and y-coordinates from the STA X1 \ heap LDA LSY2,Y STA Y1 INY \ Increment the loop counter to point to the next point JMP WPL1 \ Loop back to WPL1 for the next point in the heapName: WPLS2 [Show more] Type: Subroutine Category: Drawing planets Summary: Remove the planet from the screen Deep dive: The ball line heapContext: See this subroutine in context in the source code Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * PL2 calls WPLS2 * PL9 (Part 1 of 3) calls WPLS2

We do this by redrawing it using the lines stored in the ball line heap when the planet was originally drawn by the BLINE routine.

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Subroutine LOIN (Part 1 of 7) (category: Drawing lines)

Draw a line: Calculate the line gradient in the form of deltas

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The ball line heap pointer, which contains the number of the first free byte after the end of the LSX2 and LSY2 heaps (see the deep dive on The ball line heap for details)

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The ball line heap for storing x-coordinates (see the deep dive on The ball line heap for details)

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The ball line heap for storing y-coordinates (see the deep dive on The ball line heap for details)

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Subroutine WP1 (category: Drawing planets)

Reset the ball line heap

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Label WP2 is local to this routine

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Label WPL1 is local to this routine