draw: fix drawing of replicated source image on memlayer with a clip rectangle

when a replicated source image with a clipr with clipr.min > Pt(0, 0),
drawclip() would properly translate the src->clipr on the dstr
but then clamp the source rectangle back on src->r.

while traversing down multiple layers, this would cause the translation to
be applied multiple times to the dst rectangle giving the wrong image result.

this change adds a new drawclipnorepl() function that avoids the clamping
of source and mask rectangles to src->r and mask->r. this is then used in
libmemlayer.

the final memimagedraw() call will call drawclip() which will do the final
claming.

a testcase is provided:

#include <u.h>
#include <libc.h>
#include <draw.h>

Image *blue;
Image *red;

void
main(int, char *argv[])
{
	Image *i;

	if(initdraw(nil, nil, argv[0]) < 0)
		sysfatal("initdraw: %r");
	i = allocimage(display, screen->r, screen->chan, 1, DWhite);

	red = allocimage(display, Rect(0,0,1,1), screen->chan, 1, DRed);
	blue = allocimage(display, Rect(0,0,1,1), screen->chan, 1, DPaleblue);
	replclipr(red, 1, Rect(10, 10, 110, 110));
	replclipr(blue, 1, Rect(11, 11, 111, 111));

	/* draw on non-layer, works correctly */
	draw(i, i->r, red, nil, ZP);
	draw(i, i->r, blue, nil, ZP);
	draw(screen, screen->r, i, nil, i->r.min);
	flushimage(display, 1);

	/* draw on (screen) layer is too far to the right */
	draw(screen, screen->r, red, nil, ZP);
	draw(screen, screen->r, blue, nil, ZP);
	flushimage(display, 1);

	for(;;){
		sleep(1000);
	}
}

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/src/libmemlayer/draw.c b/sys/src/libmemlayer/draw.c
index c352a0b2c..a9c546bd9 100644
--- a/sys/src/libmemlayer/draw.c
+++ b/sys/src/libmemlayer/draw.c
@@ -42,7 +42,7 @@ ldrawop(Memimage *dst, Rectangle screenr, Rectangle clipr, void *etc, int insave
 	if(!rectinrect(r, clipr)){
 		oclipr = dst->clipr;
 		dst->clipr = clipr;
-		ok = drawclip(dst, &r, d->src, &p0, d->mask, &p1, &srcr, &mr);
+		ok = drawclipnorepl(dst, &r, d->src, &p0, d->mask, &p1, &srcr, &mr);
 		dst->clipr = oclipr;
 		if(!ok)
 			return;
@@ -74,7 +74,7 @@ if(drawdebug)	iprint("mask->layer != nil\n");
 		return;
 	}
 
-	if(drawclip(dst, &r, src, &p0, mask, &p1, &srcr, &mr) == 0){
+	if(drawclipnorepl(dst, &r, src, &p0, mask, &p1, &srcr, &mr) == 0){
 if(drawdebug)	iprint("drawclip dstcr %R srccr %R maskcr %R\n", dst->clipr, src->clipr, mask->clipr);
 		return;
 	}