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Elite on the BBC Micro

Drawing lines: LL30 (Master version)

Name: LL30 [View in context] Type: Subroutine [Compare versions] Category: Drawing lines Summary: Draw a one-segment line
Arguments: X1 The screen x-coordinate of the start of the line Y1 The screen y-coordinate of the start of the line X2 The screen x-coordinate of the end of the line Y2 The screen y-coordinate of the end of the line
.LL30 STY YSAV \ Store Y in YSAV so we can retrieve it below LDA #%00001111 \ Set bits 1 and 2 of the Access Control Register at STA VIA+&34 \ SHEILA &34 to switch screen memory into &3000-&7FFF JSR LOIN \ Draw a line from (X1, Y1) to (X2, Y2) LDA #%00001001 \ Clear bits 1 and 2 of the Access Control Register at STA VIA+&34 \ SHEILA &34 to switch main memory back into &3000-&7FFF LDY YSAV \ Retrieve the value of Y we stored above RTS \ Return from the subroutine