canvas/text.go

package canvas

import (
	"image"
	"image/color"

	"golang.org/x/image/font"
	"golang.org/x/image/math/fixed"
)

// SetFont 设置字体
func (c *Context) SetFont(face font.Face) {
	c.state.fontFace = face
}

// SetTextAlign 设置文本对齐
func (c *Context) SetTextAlign(align string) {
	c.state.textAlign = align
}

// SetTextBaseline 设置文本基线
func (c *Context) SetTextBaseline(baseline string) {
	c.state.textBaseline = baseline
}

// FillText 绘制填充文本
func (c *Context) FillText(text string, x, y float64) {
	if c.state.fontFace == nil {
		return
	}

	// 应用阴影
	if c.state.shadowBlur > 0 || c.state.shadowOffsetX != 0 || c.state.shadowOffsetY != 0 {
		c.drawTextShadow(text, x, y, true)
	}

	c.drawText(text, x, y, true)
}

// StrokeText 绘制描边文本
func (c *Context) StrokeText(text string, x, y float64) {
	if c.state.fontFace == nil {
		return
	}

	// 应用阴影
	if c.state.shadowBlur > 0 || c.state.shadowOffsetX != 0 || c.state.shadowOffsetY != 0 {
		c.drawTextShadow(text, x, y, false)
	}

	c.drawText(text, x, y, false)
}

// MeasureText 测量文本宽度
func (c *Context) MeasureText(text string) float64 {
	if c.state.fontFace == nil {
		return 0
	}

	width := 0
	for _, r := range text {
		aw, _ := c.state.fontFace.GlyphAdvance(r)
		width += aw.Round()
	}
	return float64(width)
}

// 绘制文本
func (c *Context) drawText(text string, x, y float64, fill bool) {
	pt := c.transformPoint(x, y)

	// 计算文本宽度用于对齐
	textWidth := c.MeasureText(text)

	// 应用对齐
	switch c.state.textAlign {
	case "center":
		pt.X -= int(textWidth / 2)
	case "end", "right":
		pt.X -= int(textWidth)
	}

	// 应用基线
	metrics := c.state.fontFace.Metrics()
	switch c.state.textBaseline {
	case "top":
		pt.Y += metrics.Ascent.Round()
	case "middle":
		pt.Y += (metrics.Ascent + metrics.Descent).Round() / 2
	case "bottom":
		pt.Y += metrics.Descent.Round()
	}

	// 创建文本绘制器
	drawer := font.Drawer{
		Dst:  c.img,
		Face: c.state.fontFace,
		Dot:  fixed.P(pt.X, pt.Y),
	}

	// 设置颜色
	if fill {
		switch style := c.state.fillStyle.(type) {
		case color.Color:
			drawer.Src = image.NewUniform(c.applyAlpha(style))
		case Gradient:
			drawer.Src = &gradientImage{grad: style, alpha: c.state.globalAlpha}
		}
	} else {
		// 描边文本 - 简单实现，实际应使用路径
		switch style := c.state.strokeStyle.(type) {
		case color.Color:
			drawer.Src = image.NewUniform(c.applyAlpha(style))
		case Gradient:
			drawer.Src = &gradientImage{grad: style, alpha: c.state.globalAlpha}
		}
	}

	// 绘制文本
	if fill {
		drawer.DrawString(text)
	} else {
		// 简单描边实现 - 实际应用中应使用更高级的路径方法
		offset := 1
		for dx := -offset; dx <= offset; dx++ {
			for dy := -offset; dy <= offset; dy++ {
				if dx != 0 || dy != 0 {
					drawer.Dot = fixed.P(pt.X+dx, pt.Y+dy)
					drawer.DrawString(text)
				}
			}
		}
	}
}

// 绘制文本阴影
func (c *Context) drawTextShadow(text string, x, y float64, fill bool) {
	// 保存当前状态
	c.Save()

	// 设置阴影样式
	shadowStyle := c.state.shadowColor
	c.SetFillColor(shadowStyle)
	c.SetStrokeColor(shadowStyle)
	c.SetGlobalAlpha(0.5 * c.state.globalAlpha) // 阴影透明度

	// 应用阴影偏移
	x += c.state.shadowOffsetX
	y += c.state.shadowOffsetY

	// 绘制阴影文本
	if fill {
		c.FillText(text, x, y)
	} else {
		c.StrokeText(text, x, y)
	}

	// 恢复状态
	c.Restore()
}