First implementation of scaling for retina display

Introduce a new approach that discriminate coordinates in
points and pixels. Now all the logic from the Lua side and in
rencache is to always use points. The coordinates are converted
to pixels only within the renderer, in the file renderer.c.
In this way the application logic does not need to care about the
scaling of the retina displays.

For non-retina display the scaling between points and pixels is
equal to one so nothing will change.

There is nevertheless a change that leak into the Lua side. The
subpixel coordinates are in sub-pixel, not sub-points so they are
scaled by the retina scaling factor. But no change in the code is
required because the subpixel scaling factor take into account the
retina scaling, when present.

Because the retina scaling factor is not know when the application
starts but only when a window is actually available we introduce a
mechanism to render the font with a given scaling factor only from
the renderer when they are needed. We use therefore FontDesc to
describe the font information but without actually rasterizing the
font at a given scale.

src/renderer.h

@@ -3,9 +3,9 @@
 
 #include <SDL.h>
 #include <stdint.h>
+#include "fontdesc.h"
 
 typedef struct RenImage RenImage;
-typedef struct RenFont RenFont;
 
 enum {
   RenFontAntialiasingMask = 1,
@@ -36,27 +36,29 @@ typedef struct CPReplaceTable CPReplaceTable;
 
 
 void ren_init(SDL_Window *win);
-void ren_resize();
+void ren_setup_renderer();
 void ren_update_rects(RenRect *rects, int count);
 void ren_set_clip_rect(RenRect rect);
-void ren_get_size(int *x, int *y);
+void ren_get_size(int *x, int *y); /* Reports the size in points. */
 void ren_free_window_resources();
 
 RenImage* ren_new_image(int width, int height);
 void ren_free_image(RenImage *image);
 
 RenFont* ren_load_font(const char *filename, float size, unsigned int renderer_flags);
+int ren_verify_font(const char *filename);
 void ren_free_font(RenFont *font);
 void ren_set_font_tab_size(RenFont *font, int n);
 int ren_get_font_tab_size(RenFont *font);
-int ren_get_font_width(RenFont *font, const char *text, int *subpixel_scale);
-int ren_get_font_height(RenFont *font);
-int ren_get_font_subpixel_scale(RenFont *font);
+
+int ren_get_font_width(FontDesc *font_desc, const char *text, int *subpixel_scale);
+int ren_get_font_height(FontDesc *font_desc);
+int ren_get_font_subpixel_scale(FontDesc *font_desc);
 int ren_font_subpixel_round(int width, int subpixel_scale, int orientation);
 
 void ren_draw_rect(RenRect rect, RenColor color);
-void ren_draw_text(RenFont *font, const char *text, int x, int y, RenColor color, CPReplaceTable *replacements, RenColor replace_color);
-void ren_draw_text_subpixel(RenFont *font, const char *text, int x_subpixel, int y, RenColor color, CPReplaceTable *replacements, RenColor replace_color);
+void ren_draw_text(FontDesc *font_desc, const char *text, int x, int y, RenColor color, CPReplaceTable *replacements, RenColor replace_color);
+void ren_draw_text_subpixel(FontDesc *font_desc, const char *text, int x_subpixel, int y, RenColor color, CPReplaceTable *replacements, RenColor replace_color);
 
 void ren_cp_replace_init(CPReplaceTable *rep_table);
 void ren_cp_replace_free(CPReplaceTable *rep_table);