根据背景反转油漆颜色

Question

我正在编写自定义进度条。我想创建一个类似于

的效果

其中＆＃34; 50％＆＃34;当黑条向右前进时，文本颜色动态变为白色。是否可以使用＆＃34;简单＆＃34;解决方案？我查了一下PorterDuff，ColorFilters，xFermodes，似乎没什么用。有任何想法吗？ ATM我的代码看起来像这样：

    Rect r = new Rect(1, 1, m_width-1, m_height-1);
    canvas.drawRect(r, pWhiteFill);
    r = new Rect(1, 1, progressWidth, m_height-1);
    canvas.drawRect(r, pBlackFill);     
    canvas.drawText(String.valueOf(progress)+"%", m_width/2, m_height/2, pBlackTxtM);

是否有办法修改pBlackTxtM绘画以根据在画布下方绘制的内容来更改颜色＆＃39;？

Answer 1

即使问题很老，我也想与大家分享解决方案。

你不能使用＆＃34;反转＆＃34; Paint，但您可以使用剪辑来实现它。

这个想法是两次绘制文本，一次是黑色，一次是白色，同时设置剪裁区域以匹配条的各个部分。

以下是一些概述这个想法的代码：

// store the state of the canvas, so we can restore any previous clipping
canvas.save();

// note that it's a bad idea to create the Rect during the drawing operation, better do that only once in advance
// also note that it might be sufficient and faster to draw only the white part of the bar
Rect r = new Rect(1, 1, m_width-1, m_height-1);
canvas.drawRect(r, pWhiteFill);

// this Rect should be created when the progress is set, not on every drawing operation
Rect r_black = new Rect(1, 1, progressWidth, m_height-1);
canvas.drawRect(r_black, pBlackFill);

// set the clipping region to the black part of the bar and draw the text using white ink
String text = String.valueOf(progress)+"%";
canvas.cliprect(r_black);
canvas.drawText(text, m_width/2, m_height/2, pWhiteTxtM);

// draw the same text again using black ink, setting the clipping region to the complementary part of the bar
canvas.clipRect(r, Region.Op.XOR);
canvas.drawText(text, m_width/2, m_height/2, pBlackTxtM);

canvas.restore();