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vga: implement horizontal pel panning in graphics modes

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This implements smooth scrolling, as used for example by Commander Keen
and Second Reality.

Unfortunately, this is not enough to avoid tearing in Commander Keen,
because sometimes the wrong start address is used for a frame.
On real EGA, the panning register is sampled on every line, while
the display start is latched for the next frame at the start of the
vertical retrace.  On real VGA, the panning register is also latched,
but at the end of the vertical retrace.  It looks like Keen exploits
this by only waiting for horizontal retrace when setting the display
start, but implementing it breaks the 256-color Keen games...

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2014-12-29 14:48:14 +01:00
parent 9b53b95a1c
commit 973a724eb0
4 changed files with 111 additions and 32 deletions
Download patch file Download diff file Expand all files Collapse all files

36
hw/display/vga.c
View file

@ -50,6 +50,13 @@ bool have_vga = true;
/* Address mask for non-VESA modes. */
#define VGA_VRAM_SIZE (256 * KiB)
/* This value corresponds to a shift of zero pixels
* in 9-dot text mode. In other modes, bit 3 is undefined;
* we just ignore it, so that 8 corresponds to zero pixels
* in all modes.
*/
#define VGA_HPEL_NEUTRAL 8
/*
* Video Graphics Array (VGA)
*
@ -984,8 +991,8 @@ void vga_mem_writeb(VGACommonState *s, hwaddr addr, uint32_t val)
}
}
typedef void vga_draw_line_func(VGACommonState *s1, uint8_t *d,
uint32_t srcaddr, int width);
typedef void *vga_draw_line_func(VGACommonState *s1, uint8_t *d,
uint32_t srcaddr, int width, int hpel);
#include "vga-access.h"
#include "vga-helpers.h"
@ -1052,6 +1059,8 @@ static void vga_get_params(VGACommonState *s,
params->line_offset = s->vbe_line_offset;
params->start_addr = s->vbe_start_addr;
params->line_compare = 65535;
params->hpel = VGA_HPEL_NEUTRAL;
params->hpel_split = false;
} else {
/* compute line_offset in bytes */
params->line_offset = s->cr[VGA_CRTC_OFFSET] << 3;
@ -1064,6 +1073,9 @@ static void vga_get_params(VGACommonState *s,
params->line_compare = s->cr[VGA_CRTC_LINE_COMPARE] |
((s->cr[VGA_CRTC_OVERFLOW] & 0x10) << 4) |
((s->cr[VGA_CRTC_MAX_SCAN] & 0x40) << 3);
params->hpel = s->ar[VGA_ATC_PEL];
params->hpel_split = s->ar[VGA_ATC_MODE] & 0x20;
}
}
@ -1435,6 +1447,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
ram_addr_t page0, page1, region_start, region_end;
DirtyBitmapSnapshot *snap = NULL;
int disp_width, multi_scan, multi_run;
int hpel;
uint8_t *d;
uint32_t v, addr1, addr;
vga_draw_line_func *vga_draw_line = NULL;
@ -1534,6 +1547,9 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
s->last_line_offset = s->params.line_offset;
s->last_depth = depth;
s->last_byteswap = byteswap;
/* 16 extra pixels are needed for double-width planar modes. */
s->panning_buf = g_realloc(s->panning_buf,
(disp_width + 16) * sizeof(uint32_t));
full_update = 1;
}
if (surface_data(surface) != s->vram_ptr + (s->params.start_addr * 4)
@ -1613,8 +1629,12 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
width, height, v, line_offset, s->cr[9], s->cr[VGA_CRTC_MODE],
s->params.line_compare, sr(s, VGA_SEQ_CLOCK_MODE));
#endif
hpel = bits <= 8 ? s->params.hpel : 0;
addr1 = (s->params.start_addr * 4);
bwidth = DIV_ROUND_UP(width * bits, 8);
if (hpel) {
bwidth += 4;
}
y_start = -1;
d = surface_data(surface);
linesize = surface_stride(surface);
@ -1662,7 +1682,11 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
if (y_start < 0)
y_start = y;
if (!(is_buffer_shared(surface))) {
vga_draw_line(s, d, addr, width);
uint8_t *p;
p = vga_draw_line(s, d, addr, width, hpel);
if (p) {
memcpy(d, p, disp_width * sizeof(uint32_t));
}
if (s->cursor_draw_line)
s->cursor_draw_line(s, d, y);
}
@ -1684,8 +1708,12 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
multi_run--;
}
/* line compare acts on the displayed lines */
if (y == s->params.line_compare)
if (y == s->params.line_compare) {
if (s->params.hpel_split) {
hpel = VGA_HPEL_NEUTRAL;
}
addr1 = 0;
}
d += linesize;
}
if (y_start >= 0) {