egato mulu.l d2,d4 ; d1 = d1 * d5 swap d4 ; d5 >> 16 add.w d4,d0 ; New Y -> X = 105 moveq #0,d2 NoClippingAlto: * CONTROLLO BASSO cmp.l #256,d3 ; se d3 < 256 NO CLIPPING BASSO blt.s NoClippingBasso cmp.l #256,d2 ; d3 > 256, d2 >= 256 FUORI SCREEN bge.w NO_LINEA * CLIPPING BASSO moveq #0,d4 moveq #0,d5 move.w d1,d4 ; d4 = x1 sub.w d0,d4 ; d4 = x1 - x0 move.w d3,d5 ; d5 = y1 sub.w d2,d5 ; d5 = y1 - y0 swap d4 ; d4 << 16 divs.l d5,d4 ; d4 = d5 / d4 = pre ogni Y, quante X si sposta ? sub.w #256,d3 ; 256 pixel senza clipping mulu.l d3,d4 ; d1 = d1 * d5 swap d4 ; d5 >> 16 sub.w d4,d1 ; New Y -> X = 105 move.w #255,d3 NoClippingBasso: * QUESTE SONO LE COORDINATE CALCOLATE !!! * D0 = X0 * D1 = X1 * D2 = Y0 * D3 = Y1 rts

Pagina Principale 


    Scritto da: Alfredo Ornaghi      e-mail: ted@intercom.it
                ITALY                   tel:

,N1tL> ASM Course

FILLED VECTORS (Part 3)

CLIPPING

It is used when a face comes out from the screen's visible area. By using this routine it is possible to draw only the faces's parts which are inside the screen and eliminate the ones outside.

Example: Faces to be drawed : 


             /\
            /  \
           /    \
          /      \
         /        \
         \        /
          \      /
           \    /
            \  /
             \/

Screen : 

         +---------+
         |         |
         |         |
         |         |
         |         |
         |         |
         |         |
         |         |
         |         |
         +---------+

Sum : 

            /\
           /  \
         +/----\---+
         /      \  |
        /|       \ |
        \|       / |
         \      /  |
         |\    /   |
         | \  /    |
         |  \/     |
         |         |
         +---------+

Sum with clipping : 

         +/----\---+
         /      \  |
         |       \ |
         |       / |
         \      /  |
         |\    /   |
         | \  /    |
         |  \/     |
         |         |
         +--