[Oberon] FPGA - Bitmap Paint Horizontal Line

[Tomas Kral]

Hi,

Just realised `remaining bits' on the line can be coded as  
w0 := w - (w DIV 32) * 32;

The mask is then wd*{0..w0}

Not sure I can get it any simpler.

Tomas

On Wed, 10 May 2017 11:33:19 +0200
Tomas Kral <thomas.kral at email.cz> wrote:

> Hi,
> 
> I have coded this improved version. It generally works and seems to
> handle both x, and w on bitwise level.
> 
> The main loop goes initially fast over words, and the rest by bytes.
> 
> This line `w0 := (w MOD 32) DIV 8 + 1' computes remaining bytes on
> line over MOD 32, and this clips the outstretching bits
> wd*{0..w0*8+w}.
> 
> But the above calculation seems complicated, is there an easier
> invariant I could code instead? 
> 
> `w0' can then be passed as a parameter as its value is known before
> calling to `PaintHLine'.
> 
> 
> PROCEDURE PaintHLine(x, src, dst, w: INTEGER);
>   VAR bt: BYTE; w0, w1, wd: INTEGER; pix: SET;   
> BEGIN
>  
>   (* (pix * {maskleft*8..31} * {0..maskright*8-1}) *)
> 
>   w0 := (w MOD 32) DIV 8 + 1;
>   
>   WHILE w > 0 DO
> 
>     IF w > 31 THEN SYSTEM.GET(src, wd); INC(src, 4); DEC(w, 32);
>     ELSE 
>       wd := 0; WHILE w > 0 DO SYSTEM.GET(src, bt); wd := LSL(wd,
> 8)+bt; INC(src); DEC(w, 8) END END;
> 
>     IF w < 0 THEN wd := SYSTEM.VAL(INTEGER, SYSTEM.VAL(SET,
>     wd)*{0..w0*8+w}) END;
> 
>     SYSTEM.GET(dst, pix);
>     SYSTEM.PUT(dst, SYSTEM.VAL(SET, LSL(wd, x MOD 32)) + pix);
>       
>     INC(dst, 4);
>     IF x MOD 32 > 0 THEN
>       SYSTEM.GET(dst, pix); wd := ASR(wd, -(x MOD 32));
>       SYSTEM.PUT(dst, SYSTEM.VAL(SET, wd)*{0..x MOD 32-1}+ pix)
>     END
>  
>   END
> END PaintHLine;
> 
> 



-- 
Tomas Kral <thomas.kral at email.cz>