根據背景反轉油漆顏色

Question

我正在編寫一個自定義進度欄。 我想創建類似的效果

其中“ 50％”文本顏色會動態更改為白色，而黑條向右移動。 使用“簡單”的解決方案有可能嗎？ 我查了一下PorterDuff，ColorFilters，xFermodes，似乎什么也沒用。 有任何想法嗎？ ATM我的代碼看起來像這樣：

    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);

有沒有一種方法可以修改pBlackTxtM繪畫以根據其在“畫布”上繪制的內容來更改顏色？

Answer 1

即使問題很老，我也希望分享解決方案。

您不能使用“反轉” Paint來執行此操作，但是可以使用裁剪來實現。

想法是繪制文本兩次，一次為黑色，一次為白色，同時設置剪切區域以匹配條形的各個部分。

這是一些代碼概述這個想法：

// 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();