fix(frontend): anti-alias original menu fonts before atlas upload

CMakeLists.txt

@@ -260,6 +260,7 @@ add_library(xwa_remaster STATIC
     src/xwa_remaster/original_2d.c
     src/xwa_remaster/sky_stars.c
     src/xwa_remaster/assets.c
+    src/xwa_remaster/frontend_font_aa.c
     src/xwa_remaster/text.c
 )
 if(XWA_ENABLE_DEBUG_UI)

src/xwa_remaster/assets.c

@@ -5,6 +5,7 @@
  */
 
 #include "xwa_remaster/assets.h"
+#include "xwa_remaster/frontend_font_aa.h"
 
 #include "aeron/aeron.h"
 #include "aeron/image.h"
@@ -908,7 +909,7 @@ static AeronFontGlyph* assets_copy_font_glyphs(const Xwa2dFontAtlas* source, int
 }
 
 static int assets_init_original_font(AeronCommandBuffer* cmd,
-		const Xwa2dFontAtlas* font, int atlas_scale, int generate_mips,
+		const Xwa2dFontAtlas* font, int atlas_scale, int generate_mips, int frontend_aa,
 		const char* debug_name, AeronFontAtlas* out) {
 	if (!cmd || !font || !out || atlas_scale <= 0 || font->cell_width <= 0 ||
 		font->cell_height <= 0 || font->baseline < 0 ||
@@ -918,9 +919,12 @@ static int assets_init_original_font(AeronCommandBuffer* cmd,
 		return 0;
 	AeronFontGlyph* glyphs = assets_copy_font_glyphs(font, atlas_scale);
 	int atlas_width = 0, atlas_height = 0;
-	uint8_t* atlas_rgba = glyphs ? Aeron_ImageUpscaleNearestRgba8(font->rgba, font->width, font->height,
-														  atlas_scale, &atlas_width, &atlas_height)
-								 : NULL;
+	uint8_t* atlas_rgba = glyphs ? (frontend_aa
+			? XwaFrontendFontAA_Upscale(font->rgba, font->width, font->height,
+										atlas_scale, &atlas_width, &atlas_height)
+			: Aeron_ImageUpscaleNearestRgba8(font->rgba, font->width, font->height,
+														   atlas_scale, &atlas_width, &atlas_height))
+		: NULL;
 	const int initialized = atlas_rgba && AeronFontAtlas_InitRgba8(
 			out, cmd,
 			&(AeronFontAtlasRgba8Desc) {
@@ -965,7 +969,7 @@ static AssetLoadStatus assets_load_original_flight_font(XwaRemasterAssets* a, Ae
 		return ASSET_LOAD_FAILED;
 	}
 	Xwa2dFrameSet_Free(&group);
-	if (!assets_init_original_font(cmd, &font, XWA_ORIGINAL_FONT_SCALE, 1,
+	if (!assets_init_original_font(cmd, &font, XWA_ORIGINAL_FONT_SCALE, 1, 0,
 			"XWA original flight font", &slot->atlas)) {
 		Xwa2dFontAtlas_Free(&font);
 		return ASSET_LOAD_FAILED;
@@ -1068,7 +1072,7 @@ static AssetLoadStatus assets_load_original_frontend_font(XwaRemasterAssets* a,
 			Aeron_LogWarn("xwa.remaster", "frontend font %d: original load failed: %s", font_size, error);
 		return status;
 	}
-	if (!assets_init_original_font(cmd, &font, XWA_ORIGINAL_FONT_SCALE, 0,
+	if (!assets_init_original_font(cmd, &font, XWA_ORIGINAL_FONT_SCALE, 0, 1,
 			"XWA original frontend font", &slot->atlas)) {
 		Xwa2dFontAtlas_Free(&font);
 		return ASSET_LOAD_FAILED;

src/xwa_remaster/frontend_font_aa.c

@@ -0,0 +1,61 @@
+#include "xwa_remaster/frontend_font_aa.h"
+
+#include <math.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+/* Mitchell-Netravali (B=C=1/3) reconstructs the 4x enlarged original glyph
+ * coverage without nearest-neighbour's flat pixel steps. The original ABP
+ * decoder packs glyphs with gutters; neighbouring shapes cannot bleed into
+ * one another over this 2-original-pixel support radius. */
+static float aa_kernel(float x) {
+    x = fabsf(x);
+    if (x < 1.0f)
+        return ((7.0f*x - 12.0f)*x*x + (16.0f / 3.0f)) / 6.0f;
+    if (x < 2.0f)
+        return (((-7.0f / 3.0f)*x + 12.0f)*x*x - 20.0f*x + (32.0f/3.0f)) / 6.0f;
+    return 0.0f;
+}
+
+uint8_t* XwaFrontendFontAA_Upscale(const uint8_t* rgba, int width, int height,
+                                   int scale, int* out_width, int* out_height) {
+    if (!rgba || !out_width || !out_height || width < 1 || height < 1 ||
+        scale < 1 || width > INT32_MAX / scale || height > INT32_MAX / scale)
+        return NULL;
+    const int w = width * scale, h = height * scale;
+    if ((size_t)w > SIZE_MAX / (size_t)h / 4u)
+        return NULL;
+    uint8_t* out = (uint8_t*)malloc((size_t)w * (size_t)h * 4u);
+    if (!out) return NULL;
+    for (int y = 0; y < h; ++y) {
+        const float sy = ((float)y + 0.5f) / (float)scale - 0.5f;
+        const int cy = (int)floorf(sy);
+        float wy[4];
+        for (int j = 0; j < 4; ++j)
+            wy[j] = aa_kernel(sy - (float)(cy + j - 1));
+        for (int x = 0; x < w; ++x) {
+            const float sx = ((float)x + 0.5f) / (float)scale - 0.5f;
+            const int cx = (int)floorf(sx);
+            float weighted_alpha = 0.0f;
+            for (int j = 0; j < 4; ++j) {
+                const int yy = cy + j - 1;
+                if (yy < 0 || yy >= height) continue;
+                for (int i = 0; i < 4; ++i) {
+                    const int xx = cx + i - 1;
+                    if (xx < 0 || xx >= width) continue;
+                    weighted_alpha += wy[j] * aa_kernel(sx - (float)xx) *
+                        (float)rgba[((size_t)yy * (size_t)width + (size_t)xx) * 4u + 3u];
+                }
+            }
+            if (weighted_alpha < 0.0f) weighted_alpha = 0.0f;
+            if (weighted_alpha > 255.0f) weighted_alpha = 255.0f;
+            uint8_t* pixel = out + ((size_t)y * (size_t)w + (size_t)x) * 4u;
+            pixel[0] = pixel[1] = pixel[2] = 255u;
+            pixel[3] = (uint8_t)(weighted_alpha + 0.5f);
+        }
+    }
+    *out_width = w;
+    *out_height = h;
+    return out;
+}

src/xwa_remaster/frontend_font_aa.h

@@ -0,0 +1,12 @@
+#ifndef XWA_FRONTEND_FONT_AA_H
+#define XWA_FRONTEND_FONT_AA_H
+
+#include <stdint.h>
+
+/* High-quality 4x reconstruction of decoded *frontend* ABP glyph coverage.
+ * Returns straight-alpha white ink. The atlas loader premultiplies it once.
+ * Caller owns the result; flight HUD fonts never use this function. */
+uint8_t* XwaFrontendFontAA_Upscale(const uint8_t* rgba, int width, int height,
+                                   int scale, int* out_width, int* out_height);
+
+#endif