Util: Add somewhat hacky SDF masking for outlined text rendering

include/mgba-util/image.h

@@ -159,6 +159,7 @@ void mPainterDrawRectangle(struct mPainter*, int x, int y, int width, int height
 void mPainterDrawLine(struct mPainter*, int x1, int y1, int x2, int y2);
 void mPainterDrawCircle(struct mPainter*, int x, int y, int diameter);
 void mPainterDrawMask(struct mPainter*, const struct mImage* mask, int x, int y);
+void mPainterDrawSDFMask(struct mPainter*, const struct mImage* mask, int x, int y, uint8_t upper);
 
 uint32_t mColorConvert(uint32_t color, enum mColorFormat from, enum mColorFormat to);
 uint32_t mImageColorConvert(uint32_t color, const struct mImage* from, enum mColorFormat to);

res/scripts/demos/text-demo.lua

@@ -6,6 +6,8 @@ state.painter = image.newPainter(state.overlay.image)
 state.painter:loadFont(script.dir .. "/SourceSans3-Regular.otf")
 state.painter:setFontSize(9)
 state.painter:setFill(true)
+state.painter:setStrokeWidth(1)
+state.painter:setStrokeColor(0xFF000000)
 state.painter:setBlend(true)
 
 state.painter:setFillColor(0xFFFFFFFF)
@@ -24,8 +26,9 @@ state.painter:drawText("Center right", state.width, state.height / 2, C.ALIGN.VC
 
 state.painter:setFillColor(0xFF0000FF)
 state.painter:drawText("Bottom left", 0, state.height, C.ALIGN.BOTTOM | C.ALIGN.LEFT)
-state.painter:setFillColor(0xFF000000)
-state.painter:drawText("Bottom center", state.width / 2, state.height, C.ALIGN.BOTTOM | C.ALIGN.HCENTER)
 state.painter:setFillColor(0xFF808080)
+state.painter:drawText("Bottom center", state.width / 2, state.height, C.ALIGN.BOTTOM | C.ALIGN.HCENTER)
+state.painter:setStrokeColor(0xFFFFFFFF)
+state.painter:setFillColor(0xFF000000)
 state.painter:drawText("Bottom right", state.width, state.height, C.ALIGN.BOTTOM | C.ALIGN.RIGHT)
 state.overlay:update()

src/util/image.c

@@ -904,6 +904,40 @@ void mPainterDrawMask(struct mPainter* painter, const struct mImage* mask, int x
 	}
 }
 
+void mPainterDrawSDFMask(struct mPainter* painter, const struct mImage* mask, int x, int y, uint8_t upper) {
+	if (mask->format != mCOLOR_L8) {
+		return;
+	}
+
+	COMPOSITE_BOUNDS_INIT(mask, painter->backing);
+
+	for (y = 0; y < srcRect.height; ++y) {
+		uintptr_t dstPixel = (uintptr_t) PIXEL(painter->backing, dstStartX, dstStartY + y);
+		uintptr_t maskPixel = (uintptr_t) PIXEL(mask, srcStartX, srcStartY + y);
+		for (x = 0; x < srcRect.width; ++x, dstPixel += painter->backing->depth, maskPixel += mask->depth) {
+			uint32_t color;
+			GET_PIXEL(color, maskPixel, mask->depth);
+			if (color >= upper) {
+				color = painter->fillColor;
+			} else if (color + 0x10 > upper) {
+				// TODO: Make this spread customizable without too much perf hit
+				color = ((color + 0x10 - upper) * 0x10) << 24;
+				color |= painter->fillColor & 0x00FFFFFF;
+			} else {
+				continue;
+			}
+			if (painter->blend || painter->fillColor < 0xFF000000) {
+				uint32_t current;
+				GET_PIXEL(current, dstPixel, painter->backing->depth);
+				current = mColorConvert(current, painter->backing->format, mCOLOR_ARGB8);
+				color = mColorMixARGB8(color, current);
+			}
+			color = mColorConvert(color, mCOLOR_ARGB8, painter->backing->format);
+			PUT_PIXEL(color, dstPixel, painter->backing->depth);
+		}
+	}
+}
+
 uint32_t mColorConvert(uint32_t color, enum mColorFormat from, enum mColorFormat to) {
 	if (from == to) {
 		return color;

src/util/image/font.c

@@ -11,6 +11,7 @@
 
 #include <ft2build.h>
 #include FT_FREETYPE_H
+#include FT_MODULE_H
 
 #define DPI 100
 
@@ -42,6 +43,9 @@ struct mFont* mFontOpen(const char* path) {
 		if (FT_Init_FreeType(&library)) {
 			return NULL;
 		}
+
+		FT_Int spread = 5;
+		FT_Property_Set(library, "sdf", "spread", &spread);
 	}
 
 	FT_Face face;
@@ -131,6 +135,42 @@ void mPainterDrawText(struct mPainter* painter, const char* text, int x, int y,
 		break;
 	}
 
+	if (painter->strokeWidth) {
+		int xx = x;
+		int yy = y;
+		const char* ltext = text;
+		uint32_t fillColor = painter->fillColor;
+		painter->fillColor = painter->strokeColor;
+		while (*ltext) {
+			uint32_t glyph = utf8Char((const char**) &ltext, NULL);
+
+			if (FT_Load_Char(face, glyph, FT_LOAD_DEFAULT)) {
+				continue;
+			}
+
+			if (FT_Render_Glyph(face->glyph, FT_RENDER_MODE_SDF)) {
+				continue;
+			}
+
+			struct mImage image;
+			_makeTemporaryImage(&image, &face->glyph->bitmap);
+
+			FT_Vector kerning = {0};
+			FT_Get_Kerning(face, lastGlyph, glyph, FT_KERNING_DEFAULT, &kerning);
+			xx += kerning.x;
+			yy += kerning.y;
+
+			mPainterDrawSDFMask(painter, &image, (xx >> 6) + face->glyph->bitmap_left, (yy >> 6) - face->glyph->bitmap_top, 0x70);
+			xx += face->glyph->advance.x;
+			yy += face->glyph->advance.y;
+
+			lastGlyph = glyph;
+		}
+
+		painter->fillColor = fillColor;
+		lastGlyph = 0;
+	}
+
 	while (*text) {
 		uint32_t glyph = utf8Char((const char**) &text, NULL);