Fixing scanFill overboarding

We had a problem left one the last chapter. When a path is outside the border it is possible that it overboards on the data.

Javascript Editor

What happens with scanFill? We need to check bounds when we fill the row. The following code fixes it. Run the code and then run the PostScript code above again. The rest of the t disappears.

Javascript Editor

scanFill = function (path, width, height, color, data) {
   const crossings = [];

for (var line of path) {
      var [type, x0, y0, x1, y1] = line;
      const dx = x1 - x0;
      const dy = y1 - y0;
      if (dy) {
          if (y1 < y0) { 
              [y0, y1] = [y1, y0];
              [x0, x1] = [x1, x0];
          }
          const ex = dx / dy;
          const y0c = Math.ceil(y0);
          var x = x0 + ex * (y0c - y0);
          for(var y = y0c; y < y1; y++) {
              if (y >= 0 && y < height) {
                 if (! crossings[y] ) crossings[y] = [];
                 crossings[y].push(x);
              }
              x += ex;
          }
       }
    }

for (var y in crossings) {
       const arr = crossings[y];
       arr.sort(function (a, b) { return a - b }); 
       for (var i = 0; i < arr.length - 1; i += 2) {
          var xstart = Math.floor(arr[i]);
          var xend = Math.floor(arr[i + 1]);
          var offset = ((height - 1 - y) * width + xstart) * 4;
          for (var j = xstart; j < xend; j++) {
              // we must check bounds 0 <= j < width
              if (j >= 0 && j < width) {                 
                  for (var c = 0; c < 4; c++) {
                      data[offset + c] = color[c];
                  }
              }
              offset += 4;
          }
       } 
    }

return data;

};

This quick fix added just 3 lines of code ps20240729.js

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