mask-bit.c

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/*
 
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*/
 
// Mask-bit suite. GP0(E6) sets two bits of GPU state:
//   bit 0: set-mask     - drawn pixels have VRAM bit 15 forced to 1
//   bit 1: check-mask   - skip writes to VRAM pixels with bit 15 == 1
//
// Tests:
//   1. set-mask only: drawn pixels should be 0x801f (RED + mask bit).
//   2. set-mask then check-mask overlay: mask-set pixels preserved,
//      non-mask pixels overwritten.
//
// SENTINEL OVERRIDE: the default RASTER_SENTINEL (0xDEAD) has bit 15
// set. Check-mask would skip writes to pixels containing the sentinel,
// which conflates "rasterizer chose to skip" with "sentinel collided".
// Per the documented mitigation in raster-helpers.h, this suite uses a
// local mask-clear sentinel.
 
#define MASK_SUITE_SENTINEL 0x5555u /* R=21,G=10,B=21,mask=0 - no bit 15 */
 
// clang-format off
 
CESTER_BODY(
 
// Set-mask + draw RED triangle (same as triangle A but with E6=0x01).
static void rasterDrawMaskSet(void) {
    rasterReset();
    // Use the local mask-clear sentinel so absence-tests work even
    // though check-mask is not active in this draw - keeps the suite
    // internally consistent.
    rasterFillRect(0, 0, 16, 16, MASK_SUITE_SENTINEL);
    // GP0(E6): set bit 0 (set-mask). Pixels drawn after this command
    // get VRAM bit 15 forced to 1.
    sendGPUData(0xe6000001u);
    rasterFlatTri(RASTER_CMD_RED, 0, 0, 4, 0, 0, 4);
    rasterFlushPrimitive();
}
 
// Set-mask first triangle, then check-mask second overlapping triangle.
// Geometry: tri A (0,0)(4,0)(0,4) RED with set-mask, then tri (4,0)(8,0)(4,4)
// GREEN with check-mask. They overlap on the shared edge from (4,0)
// down; mask-set RED pixels should preserve, non-overlap GREEN pixels
// should fill.
static void rasterDrawMaskCheck(void) {
    rasterReset();
    rasterFillRect(0, 0, 16, 16, MASK_SUITE_SENTINEL);
 
    // First pass: RED tri with set-mask, no check.
    sendGPUData(0xe6000001u);
    rasterFlatTri(RASTER_CMD_RED, 0, 0, 4, 0, 0, 4);
    rasterFlushPrimitive();
 
    // Second pass: GREEN tri with check-mask, no set.
    sendGPUData(0xe6000002u);
    rasterFlatTri(RASTER_CMD_GREEN, 4, 0, 8, 0, 4, 4);
    rasterFlushPrimitive();
 
    // Restore mask state to default for subsequent tests.
    sendGPUData(0xe6000000u);
}
 
)  // CESTER_BODY
 
// --------------------------------------------------------------------------
// Set-mask: drawn pixels have bit 15 forced
// --------------------------------------------------------------------------
 
CESTER_TEST(maskSet_origin_has_mask_bit, gpu_raster_phase2,
    rasterDrawMaskSet();
    ASSERT_PIXEL_EQ(EXPECT_MASK_SET_PIXEL_0_0, 0, 0);
)
 
CESTER_TEST(maskSet_interior_has_mask_bit, gpu_raster_phase2,
    rasterDrawMaskSet();
    ASSERT_PIXEL_EQ(EXPECT_MASK_SET_PIXEL_2_1, 2, 1);
)
 
CESTER_TEST(maskSet_right_edge_excluded, gpu_raster_phase2,
    rasterDrawMaskSet();
    // Note: this suite uses MASK_SUITE_SENTINEL (0x5555) not RASTER_SENTINEL.
    // The macro in raster-expected-phase2.h still references the global
    // RASTER_SENTINEL for absence cases; we override locally here.
    ASSERT_PIXEL_EQ((unsigned)MASK_SUITE_SENTINEL, 4, 0);
)
 
// --------------------------------------------------------------------------
// Check-mask: pixels already masked are preserved
// --------------------------------------------------------------------------
 
CESTER_TEST(maskCheck_preserves_red_at_overlap_1_0, gpu_raster_phase2,
    rasterDrawMaskCheck();
    // (1, 0) is in both triangles. First pass (RED + set-mask) writes
    // 0x801f. Second pass (GREEN + check-mask) should see bit 15 set
    // and skip, preserving 0x801f.
    ASSERT_PIXEL_EQ(EXPECT_MASK_CHECK_PIXEL_1_0_preserved, 1, 0);
)
 
CESTER_TEST(maskCheck_fills_green_in_non_overlap_5_0, gpu_raster_phase2,
    rasterDrawMaskCheck();
    // (5, 0) is in GREEN tri only and the local sentinel 0x5555 has bit
    // 15 clear, so check-mask should allow the write. Expect GREEN.
    ASSERT_PIXEL_EQ(EXPECT_MASK_CHECK_PIXEL_5_0_filled, 5, 0);
)