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.

data/core/docview.lua

@@ -152,10 +152,12 @@ function DocView:get_x_offset_col(line, x)
   local text = self.doc.lines[line]
 
   local xoffset, last_i, i = 0, 1, 1
+  local subpixel_scale = self:get_font():subpixel_scale();
+  local x_subpixel = subpixel_scale * x + subpixel_scale / 2
   for char in common.utf8_chars(text) do
-    local w = self:get_font():get_width(char)
-    if xoffset >= x then
-      return (xoffset - x > w / 2) and last_i or i
+    local w = self:get_font():get_width_subpixel(char)
+    if xoffset >= subpixel_scale * x then
+      return (xoffset - x_subpixel > w / 2) and last_i or i
     end
     xoffset = xoffset + w
     last_i = i

lib/font_renderer/font_renderer.h

@@ -51,8 +51,6 @@ void            FR_Blend_Glyph(FR_Renderer *font_renderer,
                     const FR_Bitmap_Glyph_Metrics *glyph, FR_Color color);
 int             FR_Subpixel_Scale(FR_Renderer *);
 
-#define FR_XADVANCE_TO_PIXELS(x, scale) (((x) + (scale) / 2) / (scale))
-
 #ifdef __cplusplus
 }
 #endif

src/api/renderer_font.c

@@ -66,7 +66,24 @@ static int f_gc(lua_State *L) {
 static int f_get_width(lua_State *L) {
   RenFont **self = luaL_checkudata(L, 1, API_TYPE_FONT);
   const char *text = luaL_checkstring(L, 2);
-  lua_pushnumber(L, ren_get_font_width(*self, text) );
+  int subpixel_scale;
+  int w = ren_get_font_width(*self, text, &subpixel_scale);
+  lua_pushnumber(L, ren_font_subpixel_round(w, subpixel_scale, 0));
+  return 1;
+}
+
+
+static int f_subpixel_scale(lua_State *L) {
+  RenFont **self = luaL_checkudata(L, 1, API_TYPE_FONT);
+  lua_pushnumber(L, ren_get_font_subpixel_scale(*self));
+  return 1;
+}
+
+
+static int f_get_width_subpixel(lua_State *L) {
+  RenFont **self = luaL_checkudata(L, 1, API_TYPE_FONT);
+  const char *text = luaL_checkstring(L, 2);
+  lua_pushnumber(L, ren_get_font_width(*self, text, NULL));
   return 1;
 }
 
@@ -79,11 +96,13 @@ static int f_get_height(lua_State *L) {
 
 
 static const luaL_Reg lib[] = {
-  { "__gc",          f_gc            },
-  { "load",          f_load          },
-  { "set_tab_width", f_set_tab_width },
-  { "get_width",     f_get_width     },
-  { "get_height",    f_get_height    },
+  { "__gc",               f_gc                 },
+  { "load",               f_load               },
+  { "set_tab_width",      f_set_tab_width      },
+  { "get_width",          f_get_width          },
+  { "get_width_subpixel", f_get_width_subpixel },
+  { "get_height",         f_get_height         },
+  { "subpixel_scale",     f_subpixel_scale     },
   { NULL, NULL }
 };
 

src/rencache.c

@@ -130,10 +130,12 @@ void rencache_draw_rect(RenRect rect, RenColor color) {
 
 
 int rencache_draw_text(RenFont *font, const char *text, int x, int y, RenColor color) {
+  int subpixel_scale;
   RenRect rect;
   rect.x = x;
   rect.y = y;
-  rect.width = ren_get_font_width(font, text);
+  int w = ren_get_font_width(font, text, &subpixel_scale);
+  rect.width = ren_font_subpixel_round(w, subpixel_scale, 0);
   rect.height = ren_get_font_height(font);
 
   if (rects_overlap(screen_rect, rect)) {

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);
 }

src/renderer.h

@@ -34,11 +34,13 @@ RenFont* ren_load_font(const char *filename, float size, unsigned int renderer_f
 void ren_free_font(RenFont *font);
 void ren_set_font_tab_width(RenFont *font, int n);
 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 ren_get_font_height(RenFont *font);
+int ren_get_font_subpixel_scale(RenFont *font);
+int ren_font_subpixel_round(int width, int subpixel_scale, int orientation);
 
 void ren_draw_rect(RenRect rect, RenColor color);
 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);
 
 #endif