我想在不改變alpha值的情況下爲像素着色。怎麼做？這不適用於我

Question

window.onload = function() { 
       var Can1 = document.getElementById('canvas2'); 

        var ctx = Can1.getContext("2d"); 
        Can1.width=960; 
        Can1.height=720; 
         //ctx.fillStyle = "rgba(0,255,0,0)"; 
         //ctx.fillRect(0,0,960,720); 
        var imgData=ctx.getImageData(0,0,960,720); 
        for (var i=0;i<imgData.data.length;i+=4) 
          { 
          imgData.data[i]=255/*-imgData.data[i]*/; 
          imgData.data[i+1]=0/*255-imgData.data[i+1]*/; 
          imgData.data[i+2]=0/*255-imgData.data[i+2]*/; 
          imgData.data[i+3]=255-imgData.data[i+3]; 
          } 
          ctx.putImageData(imgData,0,0); 




} 

Answer 1

這將更改您的畫布的每個像素爲紅色與alpha不變;

var Can1 = document.getElementById("canvas2"); 
    var ctx = Can1.getContext("2d"); 

    // get all canvas pixel data 
    imgData = ctx.getImageData(0, 0, Can1.width, Can1.height); 

    // change every pixel on the canvas to rgba(255,0,0,255); 
    for (var i=0;i<imgData.data.length;i+=4){ 
     imgData.data[i]=255  // this is the red component of this pixel 
     imgData.data[i+1]=0  // this is the green component of this pixel 
     imgData.data[i+2]=0  // this is the blue component of this pixel 
     // To keep the alpha the same, just leave .data[i+3] unchanged 
     //imgData.data[i+3]; // this is the alpha component of this pixel 
    } 

    // replace all the canvas pixels with your modified pixels 
    ctx.putImageData(imgData,0,0);