Mostly fix problem of offset with cursor positioning when using mouse

In order to get right the cursor position on text on mouse clicks it is
needed to take into account text's subpixel positioning.

This fix mostly corrects the problem but cursor positioning is still
somewhat inaccurate for long lines due to repeated commands to draw a text
along a line. Repeated draw text calls make the subpixel information
lost and small errors will add-up.

src/renderer.c

@@ -179,18 +179,20 @@ int ren_get_font_tab_width(RenFont *font) {
 }
 
 
-int ren_get_font_width(RenFont *font, const char *text) {
+int ren_get_font_width(RenFont *font, const char *text, int *subpixel_scale) {
   int x = 0;
   const char *p = text;
   unsigned codepoint;
-  const int subpixel_scale = FR_Subpixel_Scale(font->renderer);
   while (*p) {
     p = utf8_to_codepoint(p, &codepoint);
     GlyphSet *set = get_glyphset(font, codepoint);
     FR_Bitmap_Glyph_Metrics *g = &set->glyphs[codepoint & 0xff];
     x += g->xadvance;
   }
-  return FR_XADVANCE_TO_PIXELS(x, subpixel_scale);
+  if (subpixel_scale) {
+    *subpixel_scale = FR_Subpixel_Scale(font->renderer);
+  }
+  return x;
 }
 
 
@@ -282,7 +284,7 @@ void ren_draw_image(RenImage *image, RenRect *sub, int x, int y, RenColor color)
   }
 }
 
-int ren_draw_text(RenFont *font, const char *text, int x, int y, RenColor color) {
+void ren_draw_text(RenFont *font, const char *text, int x, int y, RenColor color) {
   const char *p = text;
   unsigned codepoint;
   SDL_Surface *surf = SDL_GetWindowSurface(window);
@@ -299,5 +301,22 @@ int ren_draw_text(RenFont *font, const char *text, int x, int y, RenColor color)
     }
     x_mult += g->xadvance;
   }
-  return FR_XADVANCE_TO_PIXELS(x_mult, subpixel_scale);
+}
+
+
+int ren_font_subpixel_round(int width, int subpixel_scale, int orientation) {
+  int w_mult;
+  if (orientation < 0) {
+    w_mult = width;
+  } else if (orientation == 0) {
+    w_mult = width + subpixel_scale / 2;
+  } else {
+    w_mult = width + subpixel_scale - 1;
+  }
+  return w_mult / subpixel_scale;
+}
+
+
+int ren_get_font_subpixel_scale(RenFont *font) {
+  return FR_Subpixel_Scale(font->renderer);
 }