Implement unicode character replacements

Useful to draw whitespaces with alternate characters and colors
without slowing down the text rendering.

A new API is implemented. A renderer.replacements object can be created
to list the replacements.

In turns the function renderer.draw_text and draw_text_subpixel now accept
two optional arguments for replacements.

changelog.md

@@ -6,6 +6,12 @@ This files document the changes done in Lite XL for each release.
 
 Add `system.set_window_opacity` function.
 
+Add codepoint replacement API to support natively the "draw whitespaces" option.
+It replace the `drawwhitespace` plugin. If can be configured using the
+`config.draw_whitespace` boolean variable and enabled and disables using the
+commands `draw-whitespace:toggle`, `draw-whitespace:enable`,
+`draw-whitespace:disable`.
+
 ### 1.16.5
 
 Hotfix for Github's issue https://github.com/franko/lite-xl/issues/122

data/core/command.lua

@@ -59,7 +59,7 @@ end
 
 
 function command.add_defaults()
-  local reg = { "core", "root", "command", "doc", "findreplace", "files" }
+  local reg = { "core", "root", "command", "doc", "findreplace", "files", "drawwhitespace" }
   for _, name in ipairs(reg) do
     require("core.commands." .. name)
   end

data/core/commands/drawwhitespace.lua

@@ -0,0 +1,16 @@
+local command = require "core.command"
+local config = require "core.config"
+
+command.add(nil, {
+  ["draw-whitespace:toggle"]  = function()
+    config.draw_whitespace = not config.draw_whitespace
+  end,
+
+  ["draw-whitespace:disable"] = function()
+    config.draw_whitespace = false
+  end,
+
+  ["draw-whitespace:enable"]  = function()
+    config.draw_whitespace = true
+  end,
+})

data/core/config.lua

@@ -21,6 +21,7 @@ config.max_project_files = 2000
 config.transitions = true
 config.animation_rate = 1.0
 config.blink_period = 0.8
+config.draw_whitespace = false
 
 -- Disable plugin loading setting to false the config entry
 -- of the same name.

data/core/docview.lua

@@ -314,7 +314,11 @@ function DocView:draw_line_text(idx, x, y)
   local tx, ty = subpixel_scale * x, y + self:get_line_text_y_offset()
   for _, type, text in self.doc.highlighter:each_token(idx) do
     local color = style.syntax[type]
-    tx = renderer.draw_text_subpixel(font, text, tx, ty, color)
+    if config.draw_whitespace then
+      tx = renderer.draw_text_subpixel(font, text, tx, ty, color, core.replacements, style.syntax.comment)
+    else
+      tx = renderer.draw_text_subpixel(font, text, tx, ty, color)
+    end
   end
 end
 

data/core/init.lua

@@ -345,6 +345,14 @@ function core.remove_project_directory(path)
 end
 
 
+local function whitespace_replacements()
+  local r = renderer.replacements.new()
+  r:add(" ", "·")
+  r:add("\t", "»")
+  return r
+end
+
+
 function core.init()
   command = require "core.command"
   keymap = require "core.keymap"
@@ -416,6 +424,7 @@ function core.init()
   core.redraw = true
   core.visited_files = {}
   core.restart_request = false
+  core.replacements = whitespace_replacements()
 
   core.root_view = RootView()
   core.command_view = CommandView()

src/api/api.h

@@ -6,6 +6,7 @@
 #include "lualib.h"
 
 #define API_TYPE_FONT "Font"
+#define API_TYPE_REPLACE "Replace"
 
 void api_load_libs(lua_State *L);
 

src/api/cp_replace.c

@@ -0,0 +1,42 @@
+#include "api.h"
+#include "renderer.h"
+
+
+static int f_new(lua_State *L) {
+  CPReplaceTable *rep_table = lua_newuserdata(L, sizeof(CPReplaceTable));
+  luaL_setmetatable(L, API_TYPE_REPLACE);
+  ren_cp_replace_init(rep_table);
+  return 1;
+}
+
+
+static int f_gc(lua_State *L) {
+  CPReplaceTable *rep_table = luaL_checkudata(L, 1, API_TYPE_REPLACE);
+  ren_cp_replace_free(rep_table);
+  return 0;
+}
+
+
+static int f_add(lua_State *L) {
+  CPReplaceTable *rep_table = luaL_checkudata(L, 1, API_TYPE_REPLACE);
+  const char *src = luaL_checkstring(L, 2);
+  const char *dst = luaL_checkstring(L, 3);
+  ren_cp_replace_add(rep_table, src, dst);
+  return 0;
+}
+
+
+static const luaL_Reg lib[] = {
+  { "__gc",               f_gc     },
+  { "new",                f_new    },
+  { "add",                f_add    },
+  { NULL, NULL }
+};
+
+int luaopen_renderer_replacements(lua_State *L) {
+  luaL_newmetatable(L, API_TYPE_REPLACE);
+  luaL_setfuncs(L, lib, 0);
+  lua_pushvalue(L, -1);
+  lua_setfield(L, -2, "__index");
+  return 1;
+}

src/api/renderer.c

@@ -71,28 +71,37 @@ static int f_draw_rect(lua_State *L) {
   return 0;
 }
 
-
-static int f_draw_text(lua_State *L) {
+static int draw_text_subpixel_impl(lua_State *L, bool draw_subpixel) {
   RenFont **font = luaL_checkudata(L, 1, API_TYPE_FONT);
   const char *text = luaL_checkstring(L, 2);
-  int x = luaL_checknumber(L, 3);
+  /* The coordinate below will be in subpixels iff draw_subpixel is true.
+     Otherwise it will be in pixels. */
+  int x_subpixel = luaL_checknumber(L, 3);
   int y = luaL_checknumber(L, 4);
   RenColor color = checkcolor(L, 5, 255);
-  x = rencache_draw_text(*font, text, x, y, color, false);
-  lua_pushnumber(L, x);
+
+  CPReplaceTable *rep_table;
+  RenColor replace_color;
+  if (lua_gettop(L) >= 7) {
+    rep_table = luaL_checkudata(L, 6, API_TYPE_REPLACE);
+    replace_color = checkcolor(L, 7, 255);
+  } else {
+    rep_table = NULL;
+    replace_color = (RenColor) {0};
+  }
+
+  x_subpixel = rencache_draw_text(*font, text, x_subpixel, y, color, draw_subpixel, rep_table, replace_color);
+  lua_pushnumber(L, x_subpixel);
   return 1;
 }
 
+static int f_draw_text(lua_State *L) {
+  return draw_text_subpixel_impl(L, false);
+}
+
 
 static int f_draw_text_subpixel(lua_State *L) {
-  RenFont **font = luaL_checkudata(L, 1, API_TYPE_FONT);
-  const char *text = luaL_checkstring(L, 2);
-  int x_subpixel = luaL_checknumber(L, 3);
-  int y = luaL_checknumber(L, 4);
-  RenColor color = checkcolor(L, 5, 255);
-  x_subpixel = rencache_draw_text(*font, text, x_subpixel, y, color, true);
-  lua_pushnumber(L, x_subpixel);
-  return 1;
+  return draw_text_subpixel_impl(L, true);
 }
 
 
@@ -110,10 +119,13 @@ static const luaL_Reg lib[] = {
 
 
 int luaopen_renderer_font(lua_State *L);
+int luaopen_renderer_replacements(lua_State *L);
 
 int luaopen_renderer(lua_State *L) {
   luaL_newlib(L, lib);
   luaopen_renderer_font(L);
   lua_setfield(L, -2, "font");
+  luaopen_renderer_replacements(L);
+  lua_setfield(L, -2, "replacements");
   return 1;
 }

src/meson.build

@@ -1,5 +1,6 @@
 lite_sources = [
     'api/api.c',
+    'api/cp_replace.c',
     'api/renderer.c',
     'api/renderer_font.c',
     'api/system.c',

src/rencache.c

@@ -1,3 +1,4 @@
+#include <stdint.h>
 #include <stdio.h>
 #include "rencache.h"
 
@@ -14,13 +15,16 @@
 enum { FREE_FONT, SET_CLIP, DRAW_TEXT, DRAW_RECT, DRAW_TEXT_SUBPIXEL };
 
 typedef struct {
-  int type, size;
+  int8_t type;
+  int8_t tab_size;
+  int8_t subpixel_scale;
+  int8_t x_subpixel_offset;
+  int32_t size;
   RenRect rect;
   RenColor color;
   RenFont *font;
-  short int subpixel_scale;
-  short int x_subpixel_offset;
-  int tab_size;
+  CPReplaceTable *replacements;
+  RenColor replace_color;
   char text[0];
 } Command;
 
@@ -130,7 +134,10 @@ void rencache_draw_rect(RenRect rect, RenColor color) {
   }
 }
 
-int rencache_draw_text(RenFont *font, const char *text, int x, int y, RenColor color, bool draw_subpixel) {
+int rencache_draw_text(RenFont *font,
+  const char *text, int x, int y, RenColor color, bool draw_subpixel,
+  CPReplaceTable *replacements, RenColor replace_color)
+{
   int subpixel_scale;
   int w_subpixel = ren_get_font_width(font, text, &subpixel_scale);
   RenRect rect;
@@ -150,6 +157,8 @@ int rencache_draw_text(RenFont *font, const char *text, int x, int y, RenColor c
       cmd->subpixel_scale = (draw_subpixel ? subpixel_scale : 1);
       cmd->x_subpixel_offset = x - subpixel_scale * rect.x;
       cmd->tab_size = ren_get_font_tab_size(font);
+      cmd->replacements = replacements;
+      cmd->replace_color = replace_color;
     }
   }
 
@@ -262,11 +271,14 @@ void rencache_end_frame(void) {
           break;
         case DRAW_TEXT:
           ren_set_font_tab_size(cmd->font, cmd->tab_size);
-          ren_draw_text(cmd->font, cmd->text, cmd->rect.x, cmd->rect.y, cmd->color);
+          ren_draw_text(cmd->font, cmd->text, cmd->rect.x, cmd->rect.y, cmd->color,
+            cmd->replacements, cmd->replace_color);
           break;
         case DRAW_TEXT_SUBPIXEL:
           ren_set_font_tab_size(cmd->font, cmd->tab_size);
-          ren_draw_text_subpixel(cmd->font, cmd->text, cmd->subpixel_scale * cmd->rect.x + cmd->x_subpixel_offset, cmd->rect.y, cmd->color);
+          ren_draw_text_subpixel(cmd->font, cmd->text,
+            cmd->subpixel_scale * cmd->rect.x + cmd->x_subpixel_offset, cmd->rect.y, cmd->color,
+            cmd->replacements, cmd->replace_color);
           break;
       }
     }

src/rencache.h

@@ -8,7 +8,7 @@ void rencache_show_debug(bool enable);
 void rencache_free_font(RenFont *font);
 void rencache_set_clip_rect(RenRect rect);
 void rencache_draw_rect(RenRect rect, RenColor color);
-int  rencache_draw_text(RenFont *font, const char *text, int x, int y, RenColor color, bool draw_subpixel);
+int  rencache_draw_text(RenFont *font, const char *text, int x, int y, RenColor color, bool draw_subpixel, CPReplaceTable *replacements, RenColor replace_color);
 void rencache_invalidate(void);
 void rencache_begin_frame(void);
 void rencache_end_frame(void);

src/renderer.c

@@ -6,6 +6,7 @@
 #include "font_renderer.h"
 
 #define MAX_GLYPHSET 256
+#define REPLACEMENT_CHUNK_SIZE 8
 
 struct RenImage {
   RenColor *pixels;
@@ -60,6 +61,37 @@ static const char* utf8_to_codepoint(const char *p, unsigned *dst) {
 }
 
 
+void ren_cp_replace_init(CPReplaceTable *rep_table) {
+  rep_table->size = 0;
+  rep_table->replacements = NULL;
+}
+
+
+void ren_cp_replace_free(CPReplaceTable *rep_table) {
+  free(rep_table->replacements);
+}
+
+
+void ren_cp_replace_add(CPReplaceTable *rep_table, const char *src, const char *dst) {
+  int table_size = rep_table->size;
+  if (table_size % REPLACEMENT_CHUNK_SIZE == 0) {
+    CPReplace *old_replacements = rep_table->replacements;
+    const int new_size = (table_size / REPLACEMENT_CHUNK_SIZE + 1) * REPLACEMENT_CHUNK_SIZE;
+    rep_table->replacements = malloc(new_size * sizeof(CPReplace));
+    if (!rep_table->replacements) {
+      rep_table->replacements = old_replacements;
+      return;
+    }
+    memcpy(rep_table->replacements, old_replacements, table_size * sizeof(CPReplace));
+    free(old_replacements);
+  }
+  CPReplace *rep = &rep_table->replacements[table_size];
+  utf8_to_codepoint(src, &rep->codepoint_src);
+  utf8_to_codepoint(dst, &rep->codepoint_dst);
+  rep_table->size = table_size + 1;
+}
+
+
 void ren_init(SDL_Window *win) {
   assert(win);
   window = win;
@@ -291,31 +323,55 @@ void ren_draw_image(RenImage *image, RenRect *sub, int x, int y, RenColor color)
   }
 }
 
+static int codepoint_replace(CPReplaceTable *rep_table, unsigned *codepoint) {
+  for (int i = 0; i < rep_table->size; i++) {
+    const CPReplace *rep = &rep_table->replacements[i];
+    if (*codepoint == rep->codepoint_src) {
+      *codepoint = rep->codepoint_dst;
+      return 1;
+    }
+  }
+  return 0;
+}
 
-void ren_draw_text_subpixel(RenFont *font, const char *text, int x_subpixel, int y, RenColor color) {
+
+void ren_draw_text_subpixel(RenFont *font, const char *text, int x_subpixel, int y, RenColor color,
+  CPReplaceTable *replacements, RenColor replace_color)
+{
   const char *p = text;
   unsigned codepoint;
   SDL_Surface *surf = SDL_GetWindowSurface(window);
-  FR_Color color_fr = { .r = color.r, .g = color.g, .b = color.b };
+  const FR_Color color_fr = { .r = color.r, .g = color.g, .b = color.b };
   while (*p) {
+    FR_Color color_rep;
     p = utf8_to_codepoint(p, &codepoint);
     GlyphSet *set = get_glyphset(font, codepoint);
     FR_Bitmap_Glyph_Metrics *g = &set->glyphs[codepoint & 0xff];
+    const int xadvance_original_cp = g->xadvance;
+    const int replaced = replacements ? codepoint_replace(replacements, &codepoint) : 0;
+    if (replaced) {
+      set = get_glyphset(font, codepoint);
+      g = &set->glyphs[codepoint & 0xff];
+      color_rep = (FR_Color) { .r = replace_color.r, .g = replace_color.g, .b = replace_color.b};
+    } else {
+      color_rep = color_fr;
+    }
     if (color.a != 0) {
       FR_Blend_Glyph(font->renderer, &clip,
-        x_subpixel, y, (uint8_t *) surf->pixels, surf->w, set->image, g, color_fr);
+        x_subpixel, y, (uint8_t *) surf->pixels, surf->w, set->image, g, color_rep);
     }
-    x_subpixel += g->xadvance;
+    x_subpixel += xadvance_original_cp;
   }
 }
 
-
-void 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,
+  CPReplaceTable *replacements, RenColor replace_color)
+{
   const int subpixel_scale = FR_Subpixel_Scale(font->renderer);
-  ren_draw_text_subpixel(font, text, subpixel_scale * x, y, color);
+  ren_draw_text_subpixel(font, text, subpixel_scale * x, y, color, replacements, replace_color);
 }
 
-
+// Could be declared as static inline
 int ren_font_subpixel_round(int width, int subpixel_scale, int orientation) {
   int w_mult;
   if (orientation < 0) {
@@ -332,3 +388,4 @@ int ren_font_subpixel_round(int width, int subpixel_scale, int orientation) {
 int ren_get_font_subpixel_scale(RenFont *font) {
   return FR_Subpixel_Scale(font->renderer);
 }
+

src/renderer.h

@@ -21,6 +21,19 @@ enum {
 typedef struct { uint8_t b, g, r, a; } RenColor;
 typedef struct { int x, y, width, height; } RenRect;
 
+struct CPReplace {
+  unsigned codepoint_src;
+  unsigned codepoint_dst;
+};
+typedef struct CPReplace CPReplace;
+
+
+struct CPReplaceTable {
+  int size;
+  CPReplace *replacements;
+};
+typedef struct CPReplaceTable CPReplaceTable;
+
 
 void ren_init(SDL_Window *win);
 void ren_update_rects(RenRect *rects, int count);
@@ -41,7 +54,12 @@ 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);
-void ren_draw_text(RenFont *font, const char *text, int x, int y, RenColor color);
-void ren_draw_text_subpixel(RenFont *font, const char *text, int x_subpixel, int y, 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_cp_replace_init(CPReplaceTable *rep_table);
+void ren_cp_replace_free(CPReplaceTable *rep_table);
+void ren_cp_replace_add(CPReplaceTable *rep_table, const char *src, const char *dst);
+void ren_cp_replace_clear(CPReplaceTable *rep_table);
 
 #endif