Keep 15-bit scanout independent

runtime/include/display_scanout.h

@@ -35,6 +35,20 @@ static inline uint32_t psx_display_interlaced_rows(
     return interlaced ? rows * 2u : rows;
 }
 
+/* Canvas-origin clipping belongs only to staged depth24 presentation.
+ * Ordinary 15-bit renderers read their source rectangle directly. */
+static inline uint32_t psx_display_clip_source_height(
+    int depth24, uint32_t source_height, uint32_t canvas_height,
+    uint32_t canvas_origin_y)
+{
+    if (!depth24)
+        return source_height;
+    if (canvas_origin_y >= canvas_height)
+        return 0u;
+    const uint32_t available = canvas_height - canvas_origin_y;
+    return source_height < available ? source_height : available;
+}
+
 /* Preserve the legacy default for an unset/degenerate GP1(07h) range. A
  * programmed increasing range that has no active-video intersection owns a
  * zero height instead, so presentation fails closed to black. */

runtime/src/gpu.c

@@ -3248,11 +3248,21 @@ void gpu_get_display_info(GpuDisplayInfo* out) {
 
     /* Clamp to sane maximums */
     if (w > 640) w = 640;
-    const uint32_t max_screen_h = out->depth24
-        ? PSX_DISPLAY_PRESENT_MAX_HEIGHT : 512u;
-    if (screen_h > max_screen_h) screen_h = max_screen_h;
-    if (screen_origin_y > screen_h) screen_origin_y = screen_h;
-    if (h > screen_h - screen_origin_y) h = screen_h - screen_origin_y;
+    if (out->depth24) {
+        if (screen_h > PSX_DISPLAY_PRESENT_MAX_HEIGHT)
+            screen_h = PSX_DISPLAY_PRESENT_MAX_HEIGHT;
+        if (screen_origin_y > screen_h)
+            screen_origin_y = screen_h;
+        h = psx_display_clip_source_height(
+            1, h, screen_h, screen_origin_y);
+    } else {
+        /* The active canvas is a depth24 staging contract. Keep direct 15-bit
+         * source rectangles independent from its origin and 576-row limit. */
+        if (h > 512u) h = 512u;
+        screen_h = h;
+        screen_origin_y = 0u;
+        screen_source_skip_y = 0u;
+    }
 
     out->width  = w;
     out->height = h;

runtime/tests/test_display_scanout.c

@@ -20,6 +20,9 @@ static void test_present_height(void)
     assert(psx_display_interlaced_rows(288, 0) == 288);
     assert(psx_display_interlaced_rows(288, 1) ==
            PSX_DISPLAY_PRESENT_MAX_HEIGHT);
+    assert(psx_display_clip_source_height(0, 450, 512, 126) == 450);
+    assert(psx_display_clip_source_height(1, 450, 512, 126) == 386);
+    assert(psx_display_clip_source_height(1, 450, 512, 512) == 0);
 
     PsxDisplayVerticalLayout unset = psx_display_vertical_layout(0, 100, 100);
     assert(!unset.range_set);