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Elite on the BBC Micro

Drawing lines: LL30 [Elite-A, Parasite]

Name: LL30 [Show more] Type: Subroutine Category: Drawing lines Summary: Draw a one-segment line by sending a draw_line command to the I/O processor
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * LL9 (Part 12 of 12) calls LL30 * TT15 calls LL30

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
.LOIN .LL30 LDA #&80 \ Send command &80 to the I/O processor: JSR tube_write \ \ draw_line(x1, y1, x2, y2) \ \ which will draw a line from (x1, y1) to (x2, y2) LDA X1 \ Send the first parameter to the I/O processor: JSR tube_write \ \ * x1 = X1 LDA Y1 \ Send the second parameter to the I/O processor: JSR tube_write \ \ * y1 = Y1 LDA X2 \ Send the first parameter to the I/O processor: JSR tube_write \ \ * x2 = X2 LDA Y2 \ Send the first parameter to the I/O processor: JMP tube_write \ \ * y2 = Y2 \ \ and return from the subroutine using a tail call