Adjust the font's height when creating the bitmap

Now the font's height to compute the bitmap is computed correcty but:

- STB truetype takes the pixel height as a float
- AGG takes an integer

notes.md

@@ -79,6 +79,9 @@ So BakeFontBitmap gets
 pixel_height = (ascent - descent) * font->size / unitsPerEm;
 ```
 
+In turns BakeFontBitmap passes pixel_height to ScaleForPixelHeight() and uses the
+resulting 'scale' to scale the glyphs by passing it to MakeGlyphBitmap().
+
 This is equal almost equal to font->height except the 0.5, the missing linegap calculation
 and the fact that this latter is an integer instead of a float.
 
@@ -109,54 +112,7 @@ FT_Done_FreeType (end with library)
 
 ## Freetype2's metrics related function and structs
 
-FT_New_Face
+FT_New_Face return a FT_Face (a pointer) with font face information.
-
-```c
-typedef struct  FT_FaceRec_
-{
-  FT_Long           num_faces;
-  FT_Long           face_index;
-
-  FT_Long           face_flags;
-  FT_Long           style_flags;
-
-  FT_Long           num_glyphs;
-
-  FT_String*        family_name;
-  FT_String*        style_name;
-
-  FT_Int            num_fixed_sizes;
-  FT_Bitmap_Size*   available_sizes;
-
-  FT_Int            num_charmaps;
-  FT_CharMap*       charmaps;
-
-  FT_Generic        generic;
-
-  /*# The following member variables (down to `underline_thickness`) */
-  /*# are only relevant to scalable outlines; cf. @FT_Bitmap_Size    */
-  /*# for bitmap fonts.                                              */
-  FT_BBox           bbox;
-
-  FT_UShort         units_per_EM;
-  FT_Short          ascender;
-  FT_Short          descender;
-  FT_Short          height;
-
-  FT_Short          max_advance_width;
-  FT_Short          max_advance_height;
-
-  FT_Short          underline_position;
-  FT_Short          underline_thickness;
-
-  FT_GlyphSlot      glyph;
-  FT_Size           size;
-  FT_CharMap        charmap;
-
-  /* private part omitted. */
-
-} FT_FaceRec;
-```
 
 ## AGG font engine's font size
 

tests/agg_font_render_test.cpp

@@ -25,6 +25,9 @@ struct RenFontA {
   font_renderer_alpha *renderer;
   float size;
   int height;
+  // For some reason the font's height used in renderer.c
+  // when calling BakeFontBitmap is 0.5 off from 'height'.
+  float height_bitmap;
 };
 
 template <typename T>
@@ -57,7 +60,7 @@ RenFontA* ren_load_font_agg(const char *filename, float size) {
   font = (RenFontA *) check_alloc(calloc(1, sizeof(RenFontA)));
   font->size = size;
 
-  font->renderer = new font_renderer_alpha(true, false);
+  font->renderer = new font_renderer_alpha(false, false);
   font->renderer->load_font(filename);
 
   int ascender, descender;
@@ -66,6 +69,7 @@ RenFontA* ren_load_font_agg(const char *filename, float size) {
 
   float scale = font->renderer->scale_for_em_to_pixels(size);
   font->height = (ascender - descender) * scale + 0.5;
+  font->height_bitmap = (ascender - descender) * scale;
 
   fprintf(stderr, "Font height: %d\n", font->height);
 
@@ -84,15 +88,17 @@ retry:
 
   memset(set->image->pixels, 0x00, width * height * pixel_size);
 
+  fprintf(stderr, "Using height: %g in BakeFontBitmap\n", font->height_bitmap);
+
   agg::rendering_buffer ren_buf((agg::int8u *) set->image->pixels, width, height, -width * pixel_size);
   // FIXME: figure out how to precisely layout each glyph.
-  double x = 4, y = height - font->size * 3 / 2;
+  double x = 4, y = height - font->height * 3 / 2;
   int res = 0;
   const agg::alpha8 text_color(0xff);
   for (int i = 0; i < 256; i++) {
-    if (x + font->size * 3 / 2 > width) {
+    if (x + font->height * 3 / 2 > width) {
       x = 4;
-      y -= font->size * 3 / 2;
+      y -= font->height * 3 / 2;
     }
     if (y < 0) {
       res = -1;
@@ -101,7 +107,7 @@ retry:
     // FIXME: we are ignoring idx and with a char we cannot pass codepoint > 255.
     char text[2] = {char(i % 256), 0};
     // FIXME: using font->size below is wrong.
-    font->renderer->render_text(ren_buf, font->size, text_color, x, y, text);
+    font->renderer->render_text(ren_buf, font->height_bitmap, text_color, x, y, text);
   }
 
   /* retry with a larger image buffer if the buffer wasn't large enough */

tests/stb_font_render_test.c

@@ -107,6 +107,7 @@ retry:
   float s =
     stbtt_ScaleForMappingEmToPixels(&font->stbfont, 1) /
     stbtt_ScaleForPixelHeight(&font->stbfont, 1);
+  fprintf(stderr, "Using height: %g in BakeFontBitmap\n", font->size * s);
   int res = stbtt_BakeFontBitmap(
     font->data, 0, font->size * s, (void*) set->image->pixels,
     width, height, idx * 256, 256, set->glyphs);