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LinuxJedi merged 1 commit into from
Jul 4, 2026
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denise: move the DIW comparator anchor to the hardware 2H-196 mapping #107

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23 changes: 14 additions & 9 deletions docs/internals/video.md
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Expand Up @@ -31,17 +31,20 @@ pipeline carries 24-bit colour end to end; OCS/ECS paths keep their exact
under playfield priority, and CLXDAT collisions are accumulated.
For DMA-fetched HAM playfields, the display window gates framebuffer output
and collision recording, but the low-res Denise phase can still seed the HAM
component history just before DIW: standard `$38` DDF timing starts the first
visible output one native sample into the fetched stream, so replay
pre-advances that hidden sample before painting the DIW edge. Extra fetch
component history just before DIW: when the window opens to the right of the
fetch origin (a late DIWSTRT, or an early DDFSTRT), replay pre-advances the
hidden samples before painting the DIW edge. The standard `$81` window edge
is flush with the standard `$38` picture (both at framebuffer x 62,
hardware-verified on the sblit0 A500 photo), so a stock screen hides no
samples. Extra fetch
groups from an earlier DDFSTRT are not decoded into the HAM hold colour before
DIW opens; they are fetched by Agnus, but the first visible HAM history is
bounded to the display-phase samples. Single-word lo-res fetch placement is linear in DDFSTRT: each 8-cck fetch
period before the standard `$38` slot moves the picture exactly 16 lo-res
pixels left, keeping the standard one-sample phase bias (hardware-verified
pixels left (hardware-verified
against the vAmigaTS `Agnus/DIW/OLDDIW/diw1` A500 photos, OCS and ECS).
Early and late single-word lo-res DDF both keep the standard DIW `$81`
one-sample phase; the renderer must not add or subtract a sample just to
Early and late single-word lo-res DDF keep the picture beam-anchored;
the renderer must not add or subtract a sample just to
align the picture to a fetch-unit boundary.
When DDFSTRT is late enough that DIW opens before DMA has delivered the
first BPL1DAT word for the row, playfield output remains border-colour until
Expand Down Expand Up @@ -139,9 +142,11 @@ The mapping from beam coordinates to framebuffer x is anchored by
constants that encode the hardware's fetch-to-display pipeline delays --
register writes, palette writes, and bitplane data each land at their own
documented offset, and the bitplane fetch reference differs between lo-res
and hi-res. A standard hi-res `$81` DIW with `$3C` DDF starts its 640 fetched
pixels at the display-window edge; there is no four-pixel leading border
inside the window. Wide-FMODE DMA fetches start from the revision-masked
and hi-res. The display-window comparator maps a DIWSTRT hstart H to
framebuffer x = 2H - 196 (hardware-verified against the sblit0 A500 photo).
A standard lo-res `$81`/`$38` picture is flush with that edge; a standard
hi-res `$81`/`$3C` picture starts its 640 fetched pixels one lo-res pixel
inside the window (matching vAmiga), with no wider leading border. Wide-FMODE DMA fetches start from the revision-masked
DDFSTRT comparator value and complete whole units, but the displayed shifter
origin is still quantized by the FMODE fetch gulp; the renderer keeps those
two effects separate. Denise's output line starts at the horizontal blanking
Expand Down
20 changes: 12 additions & 8 deletions src/bus.rs
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Expand Up @@ -228,20 +228,24 @@ const PAL_SPRITE_DMA_FIRST_ACTIVE_VPOS: u32 = 0x19;
const NTSC_SPRITE_DMA_FIRST_ACTIVE_VPOS: u32 = 0x14;
const RENDER_VISIBLE_LINES: usize = FB_HEIGHT;
const RENDER_FRAMEBUFFER_WIDTH: i32 = FB_WIDTH as i32;
// Capture-side twin of `bitplane::DIW_HSTART_FB0`; held 8 colour clocks (16
// lo-res pixels) left of the standard display start so the captured window
// matches vAmiga's 716-wide cutout and includes the deep-left overscan.
const RENDER_DIW_HSTART_FB0: i32 = 0x61;
// Capture-side twin of `bitplane::DIW_HSTART_FB0`; held deep left of the
// standard display start so the captured window matches vAmiga's 716-wide
// cutout and includes the deep-left overscan. Like the renderer twin, this
// puts the hardware-verified standard $81 window edge (and the sprite
// comparator positions, which share Denise's counter) at framebuffer x = 62.
const RENDER_DIW_HSTART_FB0: i32 = 0x62;
// Standard DIWSTRT $81 is the visible window edge. The first standard
// bitplane sample at DDFSTRT $38 is already one lowres native sample into the
// fetched word, so the fetch/output phase is referenced one color clock earlier.
//
// Capture-side twins of `bitplane::DIW_HSTART_FETCH_REFERENCE_*`. The hi-res
// fetch/display phase sits 3 colour clocks earlier than lo-res, so the
// reference differs by resolution (lo-res $80, hi-res $83). See the bitplane
// constant docs for the vAmiga-verified rationale.
const RENDER_DIW_HSTART_FETCH_REFERENCE_LORES: i32 = 0x80;
const RENDER_DIW_HSTART_FETCH_REFERENCE_HIRES: i32 = 0x83;
// reference differs by resolution (lo-res $81, hi-res $84). Moved +1 in
// lockstep with RENDER_DIW_HSTART_FB0 so captured bitmap positions stay at
// their hardware-calibrated framebuffer columns. See the bitplane constant
// docs for the vAmiga-verified rationale.
const RENDER_DIW_HSTART_FETCH_REFERENCE_LORES: i32 = 0x81;
const RENDER_DIW_HSTART_FETCH_REFERENCE_HIRES: i32 = 0x84;
// Capture-side twin of `bitplane::COPPER_WAIT_HPOS_FB0`; moved left by 8 colour
// clocks in lockstep with RENDER_DIW_HSTART_FB0.
const RENDER_COPPER_WAIT_HPOS_FB0: u32 = 0x28;
Expand Down
80 changes: 58 additions & 22 deletions src/bus/tests.rs
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Expand Up @@ -3399,7 +3399,9 @@ fn captured_bitplane_rows_render_after_later_dmacon_clears_bplen() {
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

assert_eq!(fb[STANDARD_VISIBLE_X0], rgb12_to_rgba8(0x0F00));
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[STANDARD_VISIBLE_X0 + 2], rgb12_to_rgba8(0x0F00));
}

#[test]
Expand Down Expand Up @@ -3442,8 +3444,13 @@ fn beam_timed_display_window_changes_clip_later_bitplane_rows() {
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

assert_eq!(fb[STANDARD_VISIBLE_X0], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[FB_WIDTH + STANDARD_VISIBLE_X0], rgb12_to_rgba8(0x0000));
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[STANDARD_VISIBLE_X0 + 2], rgb12_to_rgba8(0x0F00));
assert_eq!(
fb[FB_WIDTH + STANDARD_VISIBLE_X0 + 2],
rgb12_to_rgba8(0x0000)
);
}

#[test]
Expand Down Expand Up @@ -3563,8 +3570,10 @@ fn beam_timed_diwstrt_clips_hidden_bitplane_pixels_without_rebasing_fetch_origin
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

assert_eq!(fb[STANDARD_VISIBLE_X0 + 4], rgb12_to_rgba8(0x0000));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 6], rgb12_to_rgba8(0x0F00));
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[STANDARD_VISIBLE_X0 + 6], rgb12_to_rgba8(0x0000));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 8], rgb12_to_rgba8(0x0F00));
}

#[test]
Expand Down Expand Up @@ -3767,8 +3776,13 @@ fn beam_timed_bitplane_pointer_changes_later_fallback_fetch_rows() {
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

assert_eq!(fb[STANDARD_VISIBLE_X0], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[FB_WIDTH + STANDARD_VISIBLE_X0], rgb12_to_rgba8(0x0000));
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[STANDARD_VISIBLE_X0 + 2], rgb12_to_rgba8(0x0F00));
assert_eq!(
fb[FB_WIDTH + STANDARD_VISIBLE_X0 + 2],
rgb12_to_rgba8(0x0000)
);
}

#[test]
Expand Down Expand Up @@ -3800,7 +3814,9 @@ fn beam_timed_bitplane_pointer_changes_later_fallback_fetch_words() {
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

let x_start = STANDARD_VISIBLE_X0 + 64;
let x_start = STANDARD_VISIBLE_X0 + 66;
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[x_start], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[x_start + 32], rgb12_to_rgba8(0x0000));
}
Expand Down Expand Up @@ -4376,9 +4392,11 @@ fn beam_timed_bplcon0_hires_narrows_later_bitplane_pixels() {
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

assert_eq!(fb[STANDARD_VISIBLE_X0 + 32], rgb12_to_rgba8(0x0000));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 34], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 35], rgb12_to_rgba8(0x0000));
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[STANDARD_VISIBLE_X0 + 34], rgb12_to_rgba8(0x0000));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 36], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 37], rgb12_to_rgba8(0x0000));
}

#[test]
Expand Down Expand Up @@ -4419,9 +4437,11 @@ fn beam_timed_bplcon0_lowres_widens_later_bitplane_pixels() {
let mut fb = vec![0; FB_PIXELS];
bitplane::render(&mut bus, &mut fb);

assert_eq!(fb[STANDARD_VISIBLE_X0 + 30], rgb12_to_rgba8(0x0000));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 32], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 33], rgb12_to_rgba8(0x0F00));
// Content columns sit 2 fb px right of the hardware window edge
// (bitmap positions are beam-anchored; STANDARD_VISIBLE_X0 moved to 62).
assert_eq!(fb[STANDARD_VISIBLE_X0 + 32], rgb12_to_rgba8(0x0000));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 34], rgb12_to_rgba8(0x0F00));
assert_eq!(fb[STANDARD_VISIBLE_X0 + 35], rgb12_to_rgba8(0x0F00));
}

#[test]
Expand Down Expand Up @@ -6348,7 +6368,10 @@ fn attached_manual_sprite_data_writes_accumulate_live_sprite_sprite_clxdat() {
#[test]
fn attached_manual_sprite_odd_data_writes_accumulate_later_live_sprite_sprite_clxdat() {
let mut bus = empty_bus();
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0083);
// hstart +1 vs the pre-fix value: sprite comparator positions share
// Denise's counter and moved with the corrected window-edge anchor
// (2H-196); the beam-anchored playfield sample did not.
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0084);
bus.agnus.vpos = 0x2C;
bus.agnus.hpos = 0x38;
bus.denise.diwstrt = 0x2C83;
Expand Down Expand Up @@ -6474,7 +6497,10 @@ fn manual_sprite_position_write_on_compare_boundary_preserves_live_source() {
#[test]
fn manual_sprite_data_writes_accumulate_live_sprite_playfield_clxdat() {
let mut bus = empty_bus();
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0081);
// hstart +1 vs the pre-fix value: sprite comparator positions share
// Denise's counter and moved with the corrected window-edge anchor
// (2H-196); the beam-anchored playfield sample did not.
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0082);
bus.agnus.vpos = 0x2C;
bus.agnus.hpos = 0x38;
bus.denise.diwstrt = 0x2C81;
Expand Down Expand Up @@ -6810,11 +6836,13 @@ fn shifted_horizontal_diw_offsets_live_playfield_clxdat_fetch_origin() {
#[test]
fn denise_horizontal_delay_aligns_sprite_playfield_collision_domain() {
let display_x = live_display_window_x(0x2C81, 0x2DC1, DiwHigh::ocs_implicit()).0;
let copper_hpos = RENDER_COPPER_WAIT_HPOS_FB0 + (display_x as u32 / 4);
// The hardware window edge (62) is off the 4-px copper/register grid;
// the nearest register-domain position maps one lo-res pixel later.
let copper_hpos = RENDER_COPPER_WAIT_HPOS_FB0 + ((display_x as u32 + 2) / 4);
assert_eq!(display_x, STANDARD_VISIBLE_X0 as i32);
assert_eq!(
framebuffer_x_for_live_collision_hpos(copper_hpos),
display_x
display_x + 2
);

let row = CapturedBitplaneRow {
Expand Down Expand Up @@ -7286,7 +7314,10 @@ fn same_line_bplcon0_dual_playfield_enable_does_not_retime_earlier_live_clxdat()
fn captured_sprite_and_bitplane_rows_accumulate_live_sprite_playfield_clxdat() {
let mut bus = empty_bus();
let sprite_ptr = 0x0300usize;
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0081);
// hstart +1 vs the pre-fix value: sprite comparator positions share
// Denise's counter and moved with the corrected window-edge anchor
// (2H-196); the beam-anchored playfield sample did not.
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0082);
write_chip_word(&mut bus, sprite_ptr, pos);
write_chip_word(&mut bus, sprite_ptr + 2, ctl);
write_chip_word(&mut bus, sprite_ptr + 4, 0x8000);
Expand Down Expand Up @@ -7377,7 +7408,10 @@ fn manual_sprite_and_bpl1dat_writes_accumulate_live_sprite_playfield_clxdat() {
fn same_line_bplcon1_scroll_increase_latches_later_live_sprite_playfield_clxdat() {
let mut bus = empty_bus();
let sprite_ptr = 0x0300usize;
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0093);
// hstart +1 vs the pre-fix value: sprite comparator positions share
// Denise's counter and moved with the corrected window-edge anchor
// (2H-196); the beam-anchored playfield sample did not.
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0094);
write_chip_word(&mut bus, sprite_ptr, pos);
write_chip_word(&mut bus, sprite_ptr + 2, ctl);
write_chip_word(&mut bus, sprite_ptr + 4, 0x8000);
Expand Down Expand Up @@ -7467,7 +7501,8 @@ fn bplcon3_spres_hires_narrows_live_sprite_playfield_clxdat() {
let clxdat_after_bitplane_row_capture = |bplcon3| {
let mut bus = empty_bus();
let sprite_ptr = 0x0300usize;
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0081);
// hstart +1 vs the pre-fix value: see the sibling clxdat tests.
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0082);
write_chip_word(&mut bus, sprite_ptr, pos);
write_chip_word(&mut bus, sprite_ptr + 2, ctl);
write_chip_word(&mut bus, sprite_ptr + 4, 0x8000);
Expand Down Expand Up @@ -7512,7 +7547,8 @@ fn same_line_bplcon3_spres_write_does_not_retime_earlier_live_sprite_playfield_c
let clxdat_after_bitplane_row_capture = |spres_hpos: Option<u32>| {
let mut bus = empty_bus();
let sprite_ptr = 0x0300usize;
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0081);
// hstart +1 vs the pre-fix value: see the sibling clxdat tests.
let (pos, ctl) = sprite_control_words(0x2C, 0x2D, 0x0082);
write_chip_word(&mut bus, sprite_ptr, pos);
write_chip_word(&mut bus, sprite_ptr + 2, ctl);
write_chip_word(&mut bus, sprite_ptr + 4, 0x8000);
Expand Down
27 changes: 16 additions & 11 deletions src/video/bitplane.rs
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Expand Up @@ -35,12 +35,14 @@ use std::time::Instant;
// Denise/Agnus scheduler.
#[cfg_attr(not(test), allow(dead_code))]
const PAL_VISIBLE_LINE0: i32 = 0x2C;
// Framebuffer x=0 anchor. Held 8 colour clocks (16 lo-res pixels) left of the
// standard display start so the framebuffer captures the deep-left overscan a
// real Denise can display, matching vAmiga's 716-wide regression cutout. The
// matching shift of COPPER_WAIT_HPOS_FB0 (below) keeps the bitplane/register
// pipeline delta (BITPLANE_CONTROL_PIPELINE_FB) invariant.
const DIW_HSTART_FB0: i32 = 0x61;
// Framebuffer x=0 anchor. Held deep left of the standard display start so the
// framebuffer captures the deep-left overscan a real Denise can display,
// matching vAmiga's 716-wide regression cutout. The value pins the DIW
// comparator mapping: a DIWSTRT hstart H opens the window at framebuffer
// x = (H - this) * 2, and real hardware puts the standard $81 edge at x = 62
// (2H - 196; measured on the sblit0_A500_ECS.jpeg partial swatch columns,
// which show the bitmap's first lo-res pixel fully visible at the edge).
const DIW_HSTART_FB0: i32 = 0x62;
const STANDARD_DIW_HSTART: i32 = 0x81;
// Standard DIWSTRT $81 is the visible window edge. The first standard
// bitplane sample at DDFSTRT $38 is already one lowres native sample into the
Expand All @@ -49,12 +51,15 @@ const STANDARD_DIW_HSTART: i32 = 0x81;
// The lo-res fetch/display phase sits 3 colour clocks later than the hi-res
// phase: a hi-res fetch slot delivers its word to Denise's shifter on a
// different beam edge than a lo-res slot, so the reference the renderer uses to
// place the first fetched pixel differs by resolution. Lo-res references $80;
// hi-res references $81 so a standard $81/$3C display starts its 640 fetched
// pixels at the display-window edge instead of clipping the right edge.
// place the first fetched pixel differs by resolution. The references position
// bitplane sample 0 at framebuffer x = (reference - DIW_HSTART_FB0) * 2, so
// they moved +1 in lockstep with the DIW_HSTART_FB0 comparator fix to keep the
// hardware-calibrated bitmap positions (lo-res sample 0 at x = 62, hi-res
// standard $81/$3C flush at x = 64). The standard $81 window edge now sits at
// x = 62 too, exposing the lo-res bitmap's first sample as on real hardware.
// See `fetch_reference` below.
const DIW_HSTART_FETCH_REFERENCE_LORES: i32 = 0x80;
const DIW_HSTART_FETCH_REFERENCE_HIRES: i32 = 0x81;
const DIW_HSTART_FETCH_REFERENCE_LORES: i32 = 0x81;
const DIW_HSTART_FETCH_REFERENCE_HIRES: i32 = 0x82;
// Register/copper-write x=0 anchor, in colour clocks. Moved left by 8 colour
// clocks in lockstep with DIW_HSTART_FB0 (16 lo-res pixels) so register writes
// and bitplane pixels still register against each other after widening.
Expand Down
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