topti: support Unicode fonts

This change adds UTF-8 decoding to dtext() to fully use Unicode fonts
provided by fxconv.

src/render-cg/topti.c

@@ -42,9 +42,11 @@ static void topti_glyph(uint16_t *vram, uint32_t const * data, int left,
 		dataw - width, index);
 }
 
-void topti_render(int x, int y, char const *str, size_t size, font_t const *f,
+static void topti_render(int x, int y, char const *str_char, font_t const *f,
 	int fg, int bg)
 {
+	uint8_t const *str = (void *)str_char;
+
 	/* Raw glyph data */
 	uint32_t const *data = f->data;
 
@@ -64,15 +66,16 @@ void topti_render(int x, int y, char const *str, size_t size, font_t const *f,
 	int active_space = 0;
 
 	/* Read each character from the input string */
-	while(size--)
+	while(1)
 	{
-		int c = *str++;
+		uint32_t code_point = topti_utf8_next(&str);
+		if(!code_point) break;
 
-		int glyph = topti_glyph_index(f, c);
+		int glyph = topti_glyph_index(f, code_point);
 		if(glyph < 0) continue;
 
 		/* Draw the space if background is opaque */
-		int prop_space = (c == ' ' && f->prop) ? 5 : 0;
+		int prop_space = (code_point == ' ' && f->prop) ? 5 : 0;
 		if(active_space || prop_space)
 		{
 			active_space += prop_space;
@@ -124,5 +127,5 @@ void dtext_opt(int x, int y, int fg, int bg, int halign, int valign,
 		if(valign == DTEXT_MIDDLE) y -= ((h+1) >> 1);
 	}
 
-	topti_render(x, y, str, strlen(str), topti_font, fg, bg);
+	topti_render(x, y, str, topti_font, fg, bg);
 }

src/render-fx/topti.c

@@ -82,9 +82,11 @@ static int topti_split(uint32_t const * glyph, int width, int height, int free,
 }
 
 /* topti_render(): Render a string on the VRAM */
-void topti_render(int x, int y, char const *str, font_t const *f,
+void topti_render(int x, int y, char const *str_char, font_t const *f,
 	asm_text_t *asm_fg, asm_text_t *asm_bg, uint32_t *v1, uint32_t *v2)
 {
+	uint8_t const *str = (void *)str_char;
+
 	/* Storage height and number of free bits in operators[] */
 	int height = f->data_height, free;
 	/* Raw glyph data */
@@ -116,9 +118,12 @@ void topti_render(int x, int y, char const *str, font_t const *f,
 	v2 += (y << 2) + x;
 
 	/* Pull each character into the operator buffer */
-	while(*str)
+	while(1)
 	{
-		int glyph = topti_glyph_index(f, *str++);
+		uint32_t code_point = topti_utf8_next(&str);
+		if(!code_point) break;
+
+		int glyph = topti_glyph_index(f, code_point);
 		if(glyph < 0) continue;
 
 		int index = topti_offset(f, glyph);

src/render/render.h

@@ -26,6 +26,11 @@ extern font_t const *topti_font;
 /* Default font */
 extern font_t const *gint_default_font;
 
+/* topti_utf8_next(): Read the next UTF-8 code point of a string
+   Returns the next code point and advances the string. Returns 0 (NUL) at the
+   end of the string. */
+uint32_t topti_utf8_next(uint8_t const **str_pointer);
+
 /* topti_glyph_index(): Obtain the glyph index of a Unicode code point
    Returns the position of code_point in the character table of the given font,
    or -1 if code_point is not part of that set.

src/render/topti.c

@@ -55,9 +55,57 @@ int topti_offset(font_t const *f, uint glyph)
 	return offset;
 }
 
-/* dsize(): Get the width and height of rendered text */
-void dsize(const char *str, font_t const * f, int *w, int *h)
+/* topti_utf8_next(): Read the next UTF-8 code point of a string */
+uint32_t topti_utf8_next(uint8_t const **str_pointer)
 {
+	uint8_t const *str = *str_pointer;
+	uint8_t lead = *str++;
+
+	/* Skip non-leaders which are invalid as starting bytes */
+	while((lead >= 0x80 && lead <= 0xbf) ||
+		lead == 0xc0 || lead == 0xc1 || lead == 0xfe || lead == 0xff)
+	{
+		lead = *str++;
+	}
+
+	/* This base case will handle the NUL terminator */
+	if(lead <= 0x7f)
+	{
+		*str_pointer = str;
+		return lead;
+	}
+
+	uint8_t n2 = (*str++ & 0x3f);
+	if(lead <= 0xdf)
+	{
+		*str_pointer = str;
+		return ((lead & 0x1f) << 6) | n2;
+	}
+
+	uint8_t n3 = (*str++ & 0x3f);
+	if(lead <= 0xef)
+	{
+		*str_pointer = str;
+		return ((lead & 0x0f) << 12) | (n2 << 6) | n3;
+	}
+
+	uint8_t n4 = (*str++ & 0x3f);
+	if(lead <= 0xf7)
+	{
+		*str_pointer = str;
+		return ((lead & 0x07) << 18) | (n2 << 12) | (n3 << 6) | n4;
+	}
+
+	/* It the string is too invalid, force a space and try to continue */
+	*str_pointer = str;
+	return 0x20;
+}
+
+/* dsize(): Get the width and height of rendered text */
+void dsize(char const *str_char, font_t const * f, int *w, int *h)
+{
+	uint8_t const *str = (void *)str_char;
+
 	if(!f) f = topti_font;
 	if(h) *h = f->line_height;
 	if(!w) return;
@@ -74,17 +122,21 @@ void dsize(const char *str, font_t const * f, int *w, int *h)
 	}
 
 	/* For proportional fonts, fetch the width of each individual glyphs */
-	int width = 0, c;
+	int width = 0;
+	uint32_t code_point;
 
-	while((c = *str++))
+	while(1)
 	{
-		if(c == ' ')
+		code_point = topti_utf8_next(&str);
+		if(!code_point) break;
+
+		if(code_point == ' ')
 		{
 			width += PROP_SPACING + CHAR_SPACING;
 			continue;
 		}
 
-		int glyph = topti_glyph_index(f, c);
+		int glyph = topti_glyph_index(f, code_point);
 		if(glyph >= 0) width += f->glyph_width[glyph] + CHAR_SPACING;
 	}
 	*w = width - CHAR_SPACING;