fix: text align position

__test__/text.spec.ts

@@ -0,0 +1,37 @@
+import { readFileSync } from 'fs'
+import { join } from 'path'
+
+import ava, { TestInterface } from 'ava'
+
+import { GlobalFonts, createCanvas, Canvas, SKRSContext2D } from '../index'
+import { snapshotImage } from './image-snapshot'
+
+const test = ava as TestInterface<{
+  canvas: Canvas
+  ctx: SKRSContext2D
+}>
+
+const fontIosevka = readFileSync(join(__dirname, 'fonts', 'iosevka-slab-regular.ttf'))
+
+console.assert(GlobalFonts.register(fontIosevka), 'Register Iosevka font failed')
+
+test.beforeEach((t) => {
+  const canvas = createCanvas(512, 512)
+  t.context.canvas = canvas
+  t.context.ctx = canvas.getContext('2d')!
+})
+
+for (const align of ['center', 'end', 'left', 'right', 'start'] as CanvasTextAlign[]) {
+  test(`text-align-${align}`, async (t) => {
+    const { ctx, canvas } = t.context
+    const x = canvas.width / 2
+    ctx.strokeStyle = 'black'
+    ctx.moveTo(x, 0)
+    ctx.lineTo(x, canvas.height)
+    ctx.stroke()
+    ctx.textAlign = align
+    ctx.font = '16px Iosevka Slab'
+    ctx.fillText('Hello Canvas', 0, 200)
+    await snapshotImage(t)
+  })
+}

skia-c/skia_c.cpp

@@ -343,6 +343,7 @@ extern "C"
       float max_width,
       float x,
       float y,
+      float canvas_width,
       skiac_font_collection *c_collection,
       float font_size,
       int weight,
@@ -358,6 +359,7 @@ extern "C"
   {
     auto font_collection = c_collection->collection;
     auto font_style = SkFontStyle(weight, stretch, (SkFontStyle::Slant)slant);
+    auto text_direction = (TextDirection)direction;
     SkTArray<SkString> families;
     SkStrSplit(font_family, ",", &families);
     TextStyle text_style;
@@ -380,8 +382,7 @@ extern "C"
     ParagraphStyle paragraph_style;
     paragraph_style.turnHintingOff();
     paragraph_style.setTextStyle(text_style);
-    paragraph_style.setTextAlign((TextAlign)align);
-    paragraph_style.setTextDirection((TextDirection)direction);
+    paragraph_style.setTextDirection(text_direction);
     ParagraphBuilderImpl builder(paragraph_style, font_collection);
     builder.addText(text, text_len);
     auto paragraph = static_cast<ParagraphImpl *>(builder.Build().release());
@@ -444,8 +445,44 @@ extern "C"
 
     if (c_canvas)
     {
-      auto align_factor = 0;
-      auto paint_x = x + line_width * align_factor;
+      auto canvas_center = canvas_width / 2.0f;
+      float paint_x;
+      switch ((TextAlign)align)
+      {
+      case TextAlign::kLeft:
+        paint_x = x + canvas_center;
+        break;
+      case TextAlign::kCenter:
+        paint_x = x + canvas_center - (line_width / 2);
+        break;
+      case TextAlign::kRight:
+        paint_x = x + canvas_center - line_width;
+        break;
+      // Unreachable
+      case TextAlign::kJustify:
+        paint_x = x;
+        break;
+      case TextAlign::kStart:
+        if (text_direction == TextDirection::kLtr)
+        {
+          paint_x = x;
+        }
+        else
+        {
+          paint_x = x + canvas_width - line_width;
+        }
+        break;
+      case TextAlign::kEnd:
+        if (text_direction == TextDirection::kRtl)
+        {
+          paint_x = x;
+        }
+        else
+        {
+          paint_x = x + canvas_width - line_width;
+        }
+        break;
+      };
       auto need_scale = line_width > max_width;
       if (need_scale)
       {

skia-c/skia_c.hpp

@@ -267,6 +267,7 @@ extern "C"
       float max_width,
       float x,
       float y,
+      float canvas_width,
       skiac_font_collection *c_collection,
       float font_size,
       int weight,

src/ctx.rs

@@ -662,6 +662,7 @@ impl Context {
         x,
         y,
         max_width,
+        self.width as f32,
         weight,
         stretch as i32,
         slant,
@@ -672,7 +673,7 @@ impl Context {
         state.text_align,
         state.text_direction,
         &shadow_paint,
-      );
+      )?;
       surface.restore();
     }
 
@@ -681,6 +682,7 @@ impl Context {
       x,
       y,
       max_width,
+      self.width as f32,
       weight,
       stretch as i32,
       slant,
@@ -691,7 +693,7 @@ impl Context {
       state.text_align,
       state.text_direction,
       paint,
-    );
+    )?;
     Ok(())
   }
 
@@ -713,7 +715,7 @@ impl Context {
       state.text_align,
       state.text_direction,
       &fill_paint,
-    ));
+    )?);
     Ok(line_metrics)
   }
 

src/error.rs

@@ -1,3 +1,5 @@
+use std::ffi::NulError;
+
 use thiserror::Error;
 
 use crate::sk::Matrix;
@@ -26,6 +28,14 @@ pub enum SkError {
   U32ToStrokeJoinError(u32),
   #[error("[`{0}`] is not valid transform")]
   InvalidTransform(Matrix),
+  #[error("Convert String to CString failed")]
+  NulError,
   #[error("[`{0}`]")]
   Generic(String),
 }
+
+impl From<NulError> for SkError {
+  fn from(_: NulError) -> Self {
+    Self::NulError
+  }
+}

src/sk.rs

@@ -1,6 +1,6 @@
 use std::convert::TryFrom;
 use std::f32::consts::PI;
-use std::ffi::{c_void, CStr, CString};
+use std::ffi::{c_void, CStr, CString, NulError};
 use std::fmt;
 use std::ops::{Deref, DerefMut};
 use std::os::raw::c_char;
@@ -359,6 +359,7 @@ mod ffi {
       max_width: f32,
       x: f32,
       y: f32,
+      canvas_width: f32,
       font_collection: *mut skiac_font_collection,
       font_size: f32,
       weight: i32,
@@ -1975,6 +1976,7 @@ impl Canvas {
     x: f32,
     y: f32,
     max_width: f32,
+    canvas_width: f32,
     weight: u32,
     stretch: i32,
     slant: FontStyle,
@@ -1985,9 +1987,9 @@ impl Canvas {
     align: TextAlign,
     direction: TextDirection,
     paint: &Paint,
-  ) {
-    let c_text = std::ffi::CString::new(text).unwrap();
-    let c_font_family = std::ffi::CString::new(font_family).unwrap();
+  ) -> Result<(), NulError> {
+    let c_text = std::ffi::CString::new(text)?;
+    let c_font_family = std::ffi::CString::new(font_family)?;
 
     unsafe {
       ffi::skiac_canvas_get_line_metrics_or_draw_text(
@@ -1996,6 +1998,7 @@ impl Canvas {
         max_width,
         x,
         y,
+        canvas_width,
         font_collection.0,
         font_size,
         weight as i32,
@@ -2009,7 +2012,8 @@ impl Canvas {
         self.0,
         ptr::null_mut(),
       );
-    }
+    };
+    Ok(())
   }
 
   pub fn get_line_metrics(
@@ -2025,9 +2029,9 @@ impl Canvas {
     align: TextAlign,
     direction: TextDirection,
     paint: &Paint,
-  ) -> ffi::skiac_line_metrics {
-    let c_text = std::ffi::CString::new(text).unwrap();
-    let c_font_family = std::ffi::CString::new(font_family).unwrap();
+  ) -> Result<ffi::skiac_line_metrics, NulError> {
+    let c_text = std::ffi::CString::new(text)?;
+    let c_font_family = std::ffi::CString::new(font_family)?;
 
     let mut line_metrics = ffi::skiac_line_metrics::default();
 
@@ -2038,6 +2042,7 @@ impl Canvas {
         0.0,
         0.0,
         0.0,
+        0.0,
         font_collection.0,
         font_size,
         weight as i32,
@@ -2052,7 +2057,7 @@ impl Canvas {
         &mut line_metrics,
       );
     }
-    line_metrics
+    Ok(line_metrics)
   }
 
   pub fn draw_surface(