support ctx.direction and textAlign start/end

Author: chearon

CHANGELOG.md

@@ -13,6 +13,8 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 * Support for accessibility and links in PDFs
+* `ctx.direction` is implemented: `'rtl'` or `'ltr'` set the base direction of text
+* `ctx.textAlign` `'start'` and `'end'` are now `'right'` and `'left'` when `ctx.direction === 'rtl'`
 
 ### Fixed
 * Fix a crash in `getImageData` when the rectangle is entirely outside the canvas. ([#2024](https://github.com/Automattic/node-canvas/issues/2024))

index.d.ts

@@ -290,6 +290,7 @@ export class CanvasRenderingContext2D {
 	textBaseline: CanvasTextBaseline;
 	textAlign: CanvasTextAlign;
 	canvas: Canvas;
+	direction: 'ltr' | 'rtl';
 }
 
 export class CanvasGradient {

src/Canvas.h

@@ -37,7 +37,6 @@ enum text_align_t : int8_t {
   TEXT_ALIGNMENT_LEFT = -1,
   TEXT_ALIGNMENT_CENTER = 0,
   TEXT_ALIGNMENT_RIGHT = 1,
-  // Currently same as LEFT and RIGHT without RTL support:
   TEXT_ALIGNMENT_START = -2,
   TEXT_ALIGNMENT_END = 2
 };

src/CanvasRenderingContext2d.cc

@@ -161,7 +161,8 @@ Context2d::Initialize(Napi::Env& env, Napi::Object& exports) {
     InstanceAccessor<&Context2d::GetStrokeStyle, &Context2d::SetStrokeStyle>("strokeStyle", napi_default_jsproperty),
     InstanceAccessor<&Context2d::GetFont, &Context2d::SetFont>("font", napi_default_jsproperty),
     InstanceAccessor<&Context2d::GetTextBaseline, &Context2d::SetTextBaseline>("textBaseline", napi_default_jsproperty),
-    InstanceAccessor<&Context2d::GetTextAlign, &Context2d::SetTextAlign>("textAlign", napi_default_jsproperty)
+    InstanceAccessor<&Context2d::GetTextAlign, &Context2d::SetTextAlign>("textAlign", napi_default_jsproperty),
+    InstanceAccessor<&Context2d::GetDirection, &Context2d::SetDirection>("direction", napi_default_jsproperty)
   });
 
   exports.Set("CanvasRenderingContext2d", ctor);
@@ -230,6 +231,8 @@ Context2d::Context2d(const Napi::CallbackInfo& info) : Napi::ObjectWrap<Context2
   pango_context_set_round_glyph_positions(pango_layout_get_context(_layout), FALSE);
 #endif
 
+  pango_layout_set_auto_dir(_layout, FALSE);
+
   states.emplace();
   state = &states.top();
   pango_layout_set_font_description(_layout, state->fontDescription);
@@ -762,6 +765,27 @@ Context2d::AddPage(const Napi::CallbackInfo& info) {
   cairo_pdf_surface_set_size(canvas()->surface(), width, height);
 }
 
+/*
+ * Get text direction.
+ */
+Napi::Value
+Context2d::GetDirection(const Napi::CallbackInfo& info) {
+  return Napi::String::New(env, state->direction);
+}
+
+/*
+ * Set text direction.
+ */
+void
+Context2d::SetDirection(const Napi::CallbackInfo& info, const Napi::Value& value) {
+  if (!value.IsString()) return;
+
+  std::string dir = value.As<Napi::String>();
+  if (dir != "ltr" && dir != "rtl") return;
+
+  state->direction = dir;
+}
+
 /*
  * Put image data.
  *
@@ -2451,6 +2475,9 @@ Context2d::paintText(const Napi::CallbackInfo&info, bool stroke) {
   pango_layout_set_text(layout, str.c_str(), -1);
   pango_cairo_update_layout(context(), layout);
 
+  PangoDirection pango_dir = state->direction == "ltr" ? PANGO_DIRECTION_LTR : PANGO_DIRECTION_RTL;
+  pango_context_set_base_dir(pango_layout_get_context(_layout), pango_dir);
+
   if (argsNum == 3) {
     scaled_by = get_text_scale(layout, args[2]);
     cairo_save(context());
@@ -2522,18 +2549,26 @@ inline double getBaselineAdjustment(PangoLayout* layout, short baseline) {
 void
 Context2d::setTextPath(double x, double y) {
   PangoRectangle logical_rect;
+  text_align_t alignment = state->textAlignment;
 
-  switch (state->textAlignment) {
+  // Convert start/end to left/right based on direction
+  if (alignment == TEXT_ALIGNMENT_START) {
+    alignment = (state->direction == "rtl") ? TEXT_ALIGNMENT_RIGHT : TEXT_ALIGNMENT_LEFT;
+  } else if (alignment == TEXT_ALIGNMENT_END) {
+    alignment = (state->direction == "rtl") ? TEXT_ALIGNMENT_LEFT : TEXT_ALIGNMENT_RIGHT;
+  }
+
+  switch (alignment) {
     case TEXT_ALIGNMENT_CENTER:
       pango_layout_get_pixel_extents(_layout, NULL, &logical_rect);
       x -= logical_rect.width / 2;
       break;
-    case TEXT_ALIGNMENT_END:
     case TEXT_ALIGNMENT_RIGHT:
       pango_layout_get_pixel_extents(_layout, NULL, &logical_rect);
       x -= logical_rect.width;
       break;
-    default: ;
+    default: // TEXT_ALIGNMENT_LEFT
+      break;
   }
 
   y -= getBaselineAdjustment(_layout, state->textBaseline);
@@ -2687,13 +2722,12 @@ Napi::Value
 Context2d::GetTextAlign(const Napi::CallbackInfo& info) {
   const char* align;
   switch (state->textAlignment) {
-    default:
-    // TODO the default is supposed to be "start"
     case TEXT_ALIGNMENT_LEFT: align = "left"; break;
-    case TEXT_ALIGNMENT_START: align = "start"; break;
-    case TEXT_ALIGNMENT_CENTER: align = "center"; break;
     case TEXT_ALIGNMENT_RIGHT: align = "right"; break;
+    case TEXT_ALIGNMENT_CENTER: align = "center"; break;
+    case TEXT_ALIGNMENT_START: align = "start"; break;
     case TEXT_ALIGNMENT_END: align = "end"; break;
+    default: align = "start";
   }
   return Napi::String::New(env, align);
 }

src/CanvasRenderingContext2d.h

@@ -31,10 +31,11 @@ struct canvas_state_t {
   cairo_filter_t patternQuality = CAIRO_FILTER_GOOD;
   float globalAlpha = 1.f;
   int shadowBlur = 0;
-  text_align_t textAlignment = TEXT_ALIGNMENT_LEFT; // TODO default is supposed to be START
+  text_align_t textAlignment = TEXT_ALIGNMENT_START;
   text_baseline_t textBaseline = TEXT_BASELINE_ALPHABETIC;
   canvas_draw_mode_t textDrawingMode = TEXT_DRAW_PATHS;
   bool imageSmoothingEnabled = true;
+  std::string direction = "ltr";
 
   canvas_state_t() {
     fontDescription = pango_font_description_from_string("sans");
@@ -182,6 +183,8 @@ class Context2d : public Napi::ObjectWrap<Context2d> {
     void BeginTag(const Napi::CallbackInfo& info);
     void EndTag(const Napi::CallbackInfo& info);
     #endif
+    Napi::Value GetDirection(const Napi::CallbackInfo& info);
+    void SetDirection(const Napi::CallbackInfo& info, const Napi::Value& value);
     inline void setContext(cairo_t *ctx) { _context = ctx; }
     inline cairo_t *context(){ return _context; }
     inline Canvas *canvas(){ return _canvas; }

test/canvas.test.js

@@ -569,8 +569,6 @@ describe('Canvas', function () {
     const canvas = createCanvas(200, 200)
     const ctx = canvas.getContext('2d')
 
-    assert.equal('left', ctx.textAlign) // default TODO wrong default
-    ctx.textAlign = 'start'
     assert.equal('start', ctx.textAlign)
     ctx.textAlign = 'center'
     assert.equal('center', ctx.textAlign)