javascript - inconsistent HTML5 canvas results -


i've got following html5 javascript:

<!doctype html> <html> <head> <style> canvas {width:200px; height:200px;         border: solid blue 1px  } </style> </head> <body> <canvas id="mycanvas" ></canvas> <script> var canvas, ctx, i, tlineh = 70;  canvas = document.getelementbyid('mycanvas'); ctx = canvas.getcontext('2d');  for(i=0; i<50; i++){     ctx.linewidth = 1;     ctx.moveto(i*3+0.5, tlineh-15);     ctx.lineto(i*3+0.5, tlineh+15);     ctx.stroke(); }  for(i=200; i<240; i+=4){     ctx.linewidth = 2;     ctx.moveto(i, tlineh-30);     ctx.lineto(i, tlineh-15);     ctx.stroke(); } </script> </body> </html>

which produces first image. if reverse order of for loops second image drawn! , if change height of canvas 300px third image drawn!!

i post images here show happens don't have enough reputation points, i've put them @ https://www.dropbox.com/s/dun1vr4vjju3u7c/canvastests.png?dl=0

i'm hoping can explain why code produces different results when seems drawings should identical.

thanks, gerard

don't change width , height of canvas using css. in javascript, set with: 

ctx.canvas.height = 200; ctx.canvas.width = 200;

setting value css stretch out canvas, while setting javascript resizes it.


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