Thinko.

This introduces `FT_Library_SetLcdGeometry' for setting up arbitrary
LCD subpixel geometry including non-striped patterns.

include/freetype/freetype.h

@@ -3351,7 +3351,7 @@ FT_BEGIN_HEADER
   /*    with subpixel-rendered glyphs to prevent color-fringing!  A        */
   /*    subpixel-rendered glyph must first be filtered with a filter that  */
   /*    gives equal weight to the three color primaries and does not       */
-  /*    exceed a sum of 0x100, see section @lcd_filtering.  Then the       */
+  /*    exceed a sum of 0x100, see section @lcd_rendering.  Then the       */
   /*    only difference to gray linear blending is that subpixel-rendered  */
   /*    linear blending is done 3~times per pixel: red foreground subpixel */
   /*    to red background subpixel and so on for green and blue.           */

include/freetype/ftchapters.h

@@ -120,7 +120,7 @@
 /*    gzip                                                                 */
 /*    lzw                                                                  */
 /*    bzip2                                                                */
-/*    lcd_filtering                                                        */
+/*    lcd_rendering                                                        */
 /*                                                                         */
 /***************************************************************************/
 

include/freetype/ftlcdfil.h

@@ -36,10 +36,10 @@ FT_BEGIN_HEADER
   /***************************************************************************
    *
    * @section:
-   *   lcd_filtering
+   *   lcd_rendering
    *
    * @title:
-   *   LCD Filtering
+   *   LCD Rendering
    *
    * @abstract:
    *   Reduce color fringes of subpixel-rendered bitmaps.
@@ -298,6 +298,54 @@ FT_BEGIN_HEADER
   typedef FT_Byte  FT_LcdFiveTapFilter[FT_LCD_FILTER_FIVE_TAPS];
 
 
+  /**************************************************************************
+   *
+   * @func:
+   *   FT_Library_SetLcdGeometry
+   *
+   * @description:
+   *   This function can be used to modify default positions of color
+   *   subpixels, which controls Harmony LCD rendering.
+   *
+   * @input:
+   *   library ::
+   *     A handle to the target library instance.
+   *
+   *   sub ::
+   *     A pointer to an array of 3 vectors in 26.6 fractional pixel format;
+   *     the function modifies the default values, see the note below.
+   *
+   * @return:
+   *   FreeType error code.  0~means success.
+   *
+   * @note:
+   *   This function does nothing and returns `FT_Err_Unimplemented_Feature'
+   *   in the context of ClearType-style subpixel rendering when
+   *   FT_CONFIG_OPTION_SUBPIXEL_RENDERING is defined in your build of the
+   *   library.
+   *
+   *   Subpixel geometry examples:
+   *
+   *   - {{-21, 0}, {0, 0}, {21, 0}} is the default, corresponding 3 color
+   *   stripes shifted by a third of a pixel. This could be an RGB panel.
+   *
+   *   - {{21, 0}, {0, 0}, {-21, 0}} looks the same as the default but
+   *   offers you possibility to specify that this is a BGR panel instead,
+   *   while keeping the bitmap in the same RGB888 format.
+   *
+   *   - {{0, 21}, {0, 0}, {0, -21}} is the vertical RGB, but the bitmap
+   *   stays RGB888 as a result.
+   *
+   *   - {{32, -21}, {-32, -21}, {0, 42}} is a certain PenTile arrangement.
+   *
+   * @since:
+   *   2.9.x
+   */
+  FT_EXPORT( FT_Error )
+  FT_Library_SetLcdGeometry( FT_Library  library,
+                             FT_Vector*  sub );
+
+
   /* */
 
 

include/freetype/internal/ftobjs.h

@@ -312,11 +312,11 @@ FT_BEGIN_HEADER
   FT_CMap_Done( FT_CMap  cmap );
 
 
-  /* adds LCD padding to Min and Max boundaries */
+  /* add LCD padding to CBox */
   FT_BASE( void )
-  ft_lcd_padding( FT_Pos*       Min,
-                  FT_Pos*       Max,
-                  FT_GlyphSlot  slot );
+  ft_lcd_padding( FT_BBox*        cbox,
+                  FT_GlyphSlot    slot,
+                  FT_Render_Mode  mode );
 
 #ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
 
@@ -392,8 +392,8 @@ FT_BEGIN_HEADER
   /*                                                                       */
   /*    lcd_weights      ::                                                */
   /*    lcd_filter_func  ::                                                */
-  /*      If subpixel rendering is activated, the LCD filtering weights    */
-  /*      and callback function.                                           */
+  /*      These fields specify the LCD filtering weights and callback      */
+  /*      function for ClearType-style subpixel rendering.                 */
   /*                                                                       */
   /*    refcount ::                                                        */
   /*      A counter initialized to~1 at the time an @FT_Face structure is  */
@@ -897,11 +897,15 @@ FT_BEGIN_HEADER
   /*                        interpreter.  Currently, only the TrueType     */
   /*                        bytecode debugger uses this.                   */
   /*                                                                       */
-  /*    lcd_weights      :: If subpixel rendering is activated, the LCD    */
-  /*                        filter weights, if any.                        */
+  /*    lcd_weights      :: The LCD filter weights for ClearType-style     */
+  /*                        subpixel rendering.                            */
   /*                                                                       */
-  /*    lcd_filter_func  :: If subpixel rendering is activated, the LCD    */
-  /*                        filtering callback function.                   */
+  /*    lcd_filter_func  :: The LCD filtering callback function for        */
+  /*                        for ClearType-style subpixel rendering.        */
+  /*                                                                       */
+  /*    lcd_geometry     :: This array specifies LCD subpixel geometry     */
+  /*                        and controls Harmony LCD rendering technique,  */
+  /*                        alternative to ClearType.                      */
   /*                                                                       */
   /*    pic_container    :: Contains global structs and tables, instead    */
   /*                        of defining them globally.                     */
@@ -933,6 +937,8 @@ FT_BEGIN_HEADER
 #ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
     FT_LcdFiveTapFilter      lcd_weights;      /* filter weights, if any */
     FT_Bitmap_LcdFilterFunc  lcd_filter_func;  /* filtering callback     */
+#else
+    FT_Vector                lcd_geometry[3];  /* RGB subpixel positions */
 #endif
 
 #ifdef FT_CONFIG_OPTION_PIC

src/base/ftlcdfil.c

@@ -34,9 +34,9 @@
 
   /* add padding according to filter weights */
   FT_BASE_DEF (void)
-  ft_lcd_padding( FT_Pos*       Min,
-                  FT_Pos*       Max,
-                  FT_GlyphSlot  slot )
+  ft_lcd_padding( FT_BBox*        cbox,
+                  FT_GlyphSlot    slot,
+                  FT_Render_Mode  mode )
   {
     FT_Byte*                 lcd_weights;
     FT_Bitmap_LcdFilterFunc  lcd_filter_func;
@@ -56,10 +56,20 @@
 
     if ( lcd_filter_func == ft_lcd_filter_fir )
     {
-      *Min -= lcd_weights[0] ? 43 :
-              lcd_weights[1] ? 22 : 0;
-      *Max += lcd_weights[4] ? 43 :
-              lcd_weights[3] ? 22 : 0;
+      if ( mode == FT_RENDER_MODE_LCD )
+      {
+        cbox->xMin -= lcd_weights[0] ? 43 :
+                      lcd_weights[1] ? 22 : 0;
+        cbox->xMax += lcd_weights[4] ? 43 :
+                      lcd_weights[3] ? 22 : 0;
+      }
+      else if ( mode == FT_RENDER_MODE_LCD_V )
+      {
+        cbox->yMin -= lcd_weights[0] ? 43 :
+                      lcd_weights[1] ? 22 : 0;
+        cbox->yMax += lcd_weights[4] ? 43 :
+                      lcd_weights[3] ? 22 : 0;
+      }
     }
   }
 
@@ -341,18 +351,56 @@
     return FT_Err_Ok;
   }
 
+  FT_EXPORT_DEF( FT_Error )
+  FT_Library_SetLcdGeometry( FT_Library  library,
+                             FT_Vector*  sub )
+  {
+    FT_UNUSED( library );
+    FT_UNUSED( sub );
+
+    return FT_THROW( Unimplemented_Feature );
+  }
+
 #else /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
 
-  /* add padding according to accommodate outline shifts */
+  /* add padding to accommodate outline shifts */
   FT_BASE_DEF (void)
-  ft_lcd_padding( FT_Pos*       Min,
-                  FT_Pos*       Max,
-                  FT_GlyphSlot  slot )
+  ft_lcd_padding( FT_BBox*        cbox,
+                  FT_GlyphSlot    slot,
+                  FT_Render_Mode  mode )
   {
-    FT_UNUSED( slot );
+    FT_Vector*  sub = slot->library->lcd_geometry;
 
-    *Min -= 21;
-    *Max += 21;
+    if ( mode == FT_RENDER_MODE_LCD )
+    {
+      cbox->xMin -= FT_MAX( FT_MAX( sub[0].x, sub[1].x ), sub[2].x );
+      cbox->xMax -= FT_MIN( FT_MIN( sub[0].x, sub[1].x ), sub[2].x );
+      cbox->yMin -= FT_MAX( FT_MAX( sub[0].y, sub[1].y ), sub[2].y );
+      cbox->yMax -= FT_MIN( FT_MIN( sub[0].y, sub[1].y ), sub[2].y );
+    }
+    else if ( mode == FT_RENDER_MODE_LCD_V )
+    {
+      cbox->xMin -= FT_MAX( FT_MAX( sub[0].y, sub[1].y ), sub[2].y );
+      cbox->xMax -= FT_MIN( FT_MIN( sub[0].y, sub[1].y ), sub[2].y );
+      cbox->yMin += FT_MIN( FT_MIN( sub[0].x, sub[1].x ), sub[2].x );
+      cbox->yMax += FT_MAX( FT_MAX( sub[0].x, sub[1].x ), sub[2].x );
+    }
+  }
+
+
+  FT_EXPORT_DEF( FT_Error )
+  FT_Library_SetLcdGeometry( FT_Library  library,
+                             FT_Vector*  sub )
+  {
+    if ( !library )
+      return FT_THROW( Invalid_Library_Handle );
+
+    if ( !sub )
+      return FT_THROW( Invalid_Argument );
+
+    ft_memcpy( library->lcd_geometry, sub, 3 * sizeof( FT_Vector ) );
+
+    return FT_THROW( Unimplemented_Feature );
   }
 
 

src/base/ftobjs.c

@@ -403,12 +403,12 @@
 
     case FT_RENDER_MODE_LCD:
       pixel_mode = FT_PIXEL_MODE_LCD;
-      ft_lcd_padding( &cbox.xMin, &cbox.xMax, slot );
+      ft_lcd_padding( &cbox, slot, mode );
       goto Round;
 
     case FT_RENDER_MODE_LCD_V:
       pixel_mode = FT_PIXEL_MODE_LCD_V;
-      ft_lcd_padding( &cbox.yMin, &cbox.yMax, slot );
+      ft_lcd_padding( &cbox, slot, mode );
       goto Round;
 
     case FT_RENDER_MODE_NORMAL:

src/smooth/ftsmooth.c

@@ -31,6 +31,22 @@
   static FT_Error
   ft_smooth_init( FT_Renderer  render )
   {
+
+#ifndef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
+
+    FT_Vector*  sub = render->root.library->lcd_geometry;
+
+
+    /* set up default subpixel geometry for striped RGB panels. */
+    sub[0].x = -21;
+    sub[0].y = 0;
+    sub[1].x = 0;
+    sub[1].y = 0;
+    sub[2].x = 21;
+    sub[2].y = 0;
+
+#endif
+
     render->clazz->raster_class->raster_reset( render->raster, NULL, 0 );
 
     return 0;
@@ -235,33 +251,33 @@
       unsigned int  width  = bitmap->width;
       int           pitch  = bitmap->pitch;
 
+      FT_Vector*  sub = slot->library->lcd_geometry;
 
-      /* Render 3 separate monochrome bitmaps, shifting the outline  */
-      /* by 1/3 pixel.                                               */
+
+      /* Render 3 separate monochrome bitmaps, shifting the outline.  */
       width /= 3;
 
-      bitmap->buffer += width;
-
+      FT_Outline_Translate( outline,           -sub[0].x,           -sub[0].y );
       error = render->raster_render( render->raster, &params );
       if ( error )
         goto Exit;
 
-      FT_Outline_Translate( outline, -21, 0 );
-      x_shift        -= 21;
       bitmap->buffer += width;
-
+      FT_Outline_Translate( outline, sub[0].x - sub[1].x, sub[0].y - sub[1].y );
       error = render->raster_render( render->raster, &params );
       if ( error )
         goto Exit;
 
-      FT_Outline_Translate( outline,  42, 0 );
-      x_shift        += 42;
+      bitmap->buffer += width;
+      FT_Outline_Translate( outline, sub[1].x - sub[2].x, sub[1].y - sub[2].y );
+      error = render->raster_render( render->raster, &params );
+      if ( error )
+        goto Exit;
+
+      x_shift        -= sub[2].x;
+      y_shift        -= sub[2].y;
       bitmap->buffer -= 2 * width;
 
-      error = render->raster_render( render->raster, &params );
-      if ( error )
-        goto Exit;
-
       /* XXX: Rearrange the bytes according to FT_PIXEL_MODE_LCD.    */
       /* XXX: It is more efficient to render every third byte above. */
 
@@ -286,34 +302,36 @@
     {
       int  pitch  = bitmap->pitch;
 
+      FT_Vector*  sub = slot->library->lcd_geometry;
 
-      /* Render 3 separate monochrome bitmaps, shifting the outline  */
-      /* by 1/3 pixel. Triple the pitch to render on each third row. */
+
+      /* Render 3 separate monochrome bitmaps, shifting the outline. */
+      /* Notice that the subpixel geometry vectors are rotated.      */
+      /* Triple the pitch to render on each third row.               */
       bitmap->pitch *= 3;
       bitmap->rows  /= 3;
 
-      bitmap->buffer += pitch;
-
+      FT_Outline_Translate( outline,           -sub[0].y, sub[0].x            );
       error = render->raster_render( render->raster, &params );
       if ( error )
         goto Exit;
 
-      FT_Outline_Translate( outline, 0,  21 );
-      y_shift        += 21;
       bitmap->buffer += pitch;
-
+      FT_Outline_Translate( outline, sub[0].y - sub[1].y, sub[1].x - sub[0].x );
       error = render->raster_render( render->raster, &params );
       if ( error )
         goto Exit;
 
-      FT_Outline_Translate( outline, 0, -42 );
-      y_shift        -= 42;
+      bitmap->buffer += pitch;
+      FT_Outline_Translate( outline, sub[1].y - sub[2].y, sub[2].x - sub[1].x );
+      error = render->raster_render( render->raster, &params );
+      if ( error )
+        goto Exit;
+
+      x_shift        -= sub[2].y;
+      y_shift        += sub[2].x;
       bitmap->buffer -= 2 * pitch;
 
-      error = render->raster_render( render->raster, &params );
-      if ( error )
-        goto Exit;
-
       bitmap->pitch /= 3;
       bitmap->rows  *= 3;
     }