On Thu, 15 Jan 2026, Chad Jablonski wrote:
Use scissor registers to clip blit operations. This is required
for text rendering in X using the r128 driver. Without it overly-wide
glyphs are drawn and create all sorts of chaos.
The visible destination rectangle (vis_dst) is the intersection of the
scissor rectangle and the destination rectangle (dst.rect).
The src also needs to be offset if clipped on the top and/or
left sides to ensure that src data is read correctly and appears
clipped when drawn rather than shifted.
Signed-off-by: Chad Jablonski <[email protected]>
---
hw/display/ati_2d.c | 81 ++++++++++++++++++++++++++++-----------------
1 file changed, 50 insertions(+), 31 deletions(-)
diff --git a/hw/display/ati_2d.c b/hw/display/ati_2d.c
index 691e0f0702..a5dc5ba98e 100644
--- a/hw/display/ati_2d.c
+++ b/hw/display/ati_2d.c
@@ -86,7 +86,8 @@ static void ati_2d_do_blt(ATIVGAState *s, const ATIBltSrc
*src, ATIBltDst *dst)
/* rewritten but for now as a start just to get some output: */
DisplaySurface *ds = qemu_console_surface(s->vga.con);
uint8_t *end = s->vga.vram_ptr + s->vga.vram_size;
- int dst_stride_words, src_stride_words;
+ int dst_stride_words, src_stride_words, vis_src_x, vis_src_y;
+ QemuRect scissor, vis_dst;
DPRINTF("%p %u ds: %p %d %d rop: %x\n", s->vga.vram_ptr,
s->vga.vbe_start_addr, surface_data(ds), surface_stride(ds),
@@ -108,14 +109,32 @@ static void ati_2d_do_blt(ATIVGAState *s, const ATIBltSrc
*src, ATIBltDst *dst)
return;
}
+ qemu_rect_init(&scissor,
+ s->regs.sc_left, s->regs.sc_top,
+ s->regs.sc_right - s->regs.sc_left + 1,
+ s->regs.sc_bottom - s->regs.sc_top + 1);
+ qemu_rect_intersect(&dst->rect, &scissor, &vis_dst);
Is there a bit somewhere that enables clipping that needs to be checked
here? Or are the sc regs always expected to have meaningful values and
clipping is always done?
+ if (!vis_dst.height || !vis_dst.width) {
+ /* Nothing to do, completely clipped */
It's less clear what vis means so maybe this comment could clarify by
saying Nothing is visible, completely clipped.
Regards,
BALATON Zoltan
