android - 根据背景反转油漆颜色

Question

我正在写一个自定义进度条。我想创建一个类似于

的效果

其中“50%”文本颜色动态变为白色，同时黑色条向右移动。这可能使用“简单”的解决方案吗？我查找了 PorterDuff、ColorFilters、xFermodes，似乎没有任何效果。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);

有没有一种方法可以修改 pBlackTxtM 绘制以根据“ Canvas 上”下方绘制的内容更改颜色？

Answer 1

即使这个问题很老，我也想分享解决方案。

您不能使用“反转”Paint 来做到这一点，但您可以使用裁剪来实现它。

想法是绘制文本两次，一次是黑色，一次是白色，同时设置剪裁区域以匹配栏的相应部分。

这里有一些代码来概述这个想法:

// 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();