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⌂ ∞ Lander on the Acorn Archimedes

Drawing triangles: DrawTriangleFromBuffer

       Name: DrawTriangleFromBuffer                                  [Show more]
       Type: Subroutine
   Category: Drawing triangles
    Summary: Process the "draw triangle" command from the graphics buffer
  Deep dive: Depth-sorting with the graphics buffers
             Drawing triangles

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * bufferJump calls DrawTriangleFromBuffer




 The seven parameter words for this command match the arguments for the
 DrawTriangle routine:

   * Pixel coordinate of corner 1 (x1, y1)
   * Pixel coordinate of corner 2 (x2, y2)
   * Pixel coordinate of corner 3 (x3, y3)
   * Colour

 This command draws a triangle of the specified shape and colour.



 Arguments:

   R9                               The address of the seven parameter words in
                                    the graphics buffer



 Returns:

   R9                               Updated to point to the next word in the
                                    graphics buffer

   R12                              R12 is preserved



.DrawTriangleFromBuffer

 LDMIA   R9!, {R0-R5, R8}           \ Fetch the seven parameter words from the
                                    \ graphics buffer into R0 to R5 and R8,
                                    \ incrementing R9 to point to the next
                                    \ command in the buffer

 STMFD   R13!, {R9, R12}            \ Store R9 and R12 on the stack so they
                                    \ don't get corrupted by the following call
                                    \ to DrawTriangle

 BL      DrawTriangle               \ Draw a triangle at the coordinates
                                    \ specified in R0 to R5 and R8

 LDMFD   R13!, {R9, R12}            \ Retrieve the values of R9 and R12 that we
                                    \ stored above

 B       DrawNextFromGraphicsBuffer \ Draw the next command from the graphics
                                    \ buffer