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VisualizaçõesUnpredictable behaviour of HTML canvas
I observe weird behaviour of HTML canvas both in chrome and in firefox. For some reason there is one-pixel wide palid line when I fill rect over the smaller rect of different color after clipping.
Here is JS fiddle snippet: https://jsfiddle.net/srkgbxw1/7/
var my_canvas = document.getElementById('canvas'),
context = my_canvas.getContext("2d");
context.translate(0.5, 0.5)
context.fillStyle = "orange";
context.fillRect(10,10,100,100);
context.beginPath();
context.rect(20,20,90,90);
context.clip();
context.fillStyle = "white";
context.fillRect(0,0,110,110);
context.fillStyle = "orange";
context.fillRect(0,0,190,190);
This is the result:
Please help me figure out what the reason for the pallid line after third fillRect with orange?
UPD: original question's changed after I was pointed out I had made a stupid mistake in its first edition
UPD 2 I got the answer, this happens due to color interpolation at edges of clipping region because context was translated for half a pixel, which was done to get thin lines (recommended technique). To avoid interpolation, clipping region should be adjusted for half a pixel as well, then the pallid line disappears.
1 Respostas
Responde à pergunta0
If you look into the logs:
TypeError: context.setStrokeStyle is not a function
Therefore, when you comment it, everything after it is executed while when you uncomment it, it fails and everything after this line is not executed.
EDIT: For the second question issue:
The issue is equivalent to this, why the blue square does not fully overlap the red square:
context.translate(0.5, 0.5);
context.fillStyle = "red";
context.fillRect(10,10,100,100);
context.fillStyle = "blue";
context.fillRect(10,10,100,100);
Because of translate, you are now drawing in float pixels, everything moved by half a pixel. I suggest you read this for more information about how it is handled: fillRect() not overlapping exactly when float numbers are used
Removing context.translate(0.5, 0.5); removes the "palid line".