Make the FontRenderer's Bitmap struct opaque outside the library

lib/font_renderer/font_renderer.h

@@ -12,13 +12,7 @@ typedef struct {
   float xoff, yoff, xadvance;
 } GlyphBitmapInfo;
 
-// Important: when a subpixel scale is used the width below will be the width in logical pixel.
-// As each logical pixel contains 3 subpixels it means that the 'pixels' pointer
-// will hold enough space for '3 * width' uint8_t values.
-typedef struct {
-  uint8_t *pixels;
-  int width, height;
-} FontRendererBitmap;
+typedef struct FontRendererBitmap FontRendererBitmap;
 
 struct FontRendererImpl;
 typedef struct FontRendererImpl FontRenderer;
@@ -46,7 +40,7 @@ int             FontRendererLoadFont(FontRenderer *, const char *filename);
 int             FontRendererGetFontHeight(FontRenderer *, float size);
 
 int             FontRendererBakeFontBitmap(FontRenderer *, int font_height,
-                    void *pixels, int pixels_width, int pixels_height,
+                    FontRendererBitmap *image,
                     int first_char, int num_chars, GlyphBitmapInfo *glyph_info,
                     int subpixel_scale);
 
@@ -65,6 +59,10 @@ void            FontRendererBlendGammaSubpixel(FontRenderer *font_renderer,
                     const FontRendererBitmap *glyphs_bitmap,
                     const GlyphBitmapInfo *glyph, FontRendererColor color);
 
+FontRendererBitmap* FontRendererBitmapNew(int width, int height, int subpixel_scale);
+
+void FontRendererBitmapFree(FontRendererBitmap *image);
+
 #ifdef __cplusplus
 }
 #endif