在缩放的画布上测量文本

Question

我一直在努力学习文本测量和缩放画布.

当画布未缩放时,getTextBounds和measureText可以提供准确的结果.但是,当缩放画布时,两种方法都不会提供与打印文本的实际大小相匹配的结果.

为了测试,我使用以下onDraw方法创建了View的子类:

final float scaling = 0.51f;
final int fontSize = 50;

canvas.scale(scaling, scaling);
font = Typeface.create("Arial", Typeface.NORMAL);

Paint paint = new Paint();
paint.setColor(0xff4444ff);
paint.setTypeface(font);
paint.setTextSize(fontSize);
paint.setAntiAlias(true);

int x = 10;
int y = 100;
final String text = "Lorem ipsum dolor sit amet, consectetur adipisici elit...";
canvas.drawText(text, x, y, paint);

// draw border using getTextBounds

paint.setColor(0xffff0000);
paint.setStyle(Paint.Style.STROKE);
paint.setTypeface(font);
paint.setTextSize(fontSize);
Rect bounds = new Rect();
paint.getTextBounds(text, 0, text.length(), bounds);
bounds.offset(x, y);
paint.setColor(0x80ffff00);
canvas.drawRect(bounds, paint);

// draw border using measureText

float w = paint.measureText(text);
bounds.left = x;
bounds.right = (int) Math.ceil(bounds.left + w);
bounds.top -= 10;
bounds.bottom += 10;
paint.setColor(0x8000ffff);
paint.setPathEffect(new DashPathEffect(new float[] { 10, 10 }, 0));
canvas.drawRect(bounds, paint);

对于缩放= 0.5我得到以下输出:

对于缩放= 0.51,显示以下结果:

黄色实线边框标记从getTextBounds传送的rect,使用measureText传送的宽度呈现虚线青色rect.

如您所见,缩放= 0.5的文本小于测量的尺寸,缩放= 0.51,绘制的文本大于测量的尺寸.

任何帮助表示赞赏!

Answer 1

好吧，刚刚知道如何规避这个问题。

问题是 Paint 不知道 Canvas 缩放。因此，measureText 和 getTextBounds 提供未缩放的结果。但由于字体大小不会线性缩放（但是，绘制的矩形会线性缩放），因此您必须手动弥补该影响。

所以解决方案是：

// paint the text as usual
Paint paint = new Paint();
paint.setTypeface(font);
paint.setTextSize(fontSize);
canvas.drawText(text, x, y, paint);


// measure the text using scaled font size and correct the scaled value afterwards
Paint paint = new Paint();
paint.setTypeface(font);
paint.setTextSize(fontSize * scaling);
float w = paint.measureText(text) / scaling;