javascript - HTML5 Canvas - fillRect() vs rect()

Question

In the code below, the second fillStyle overrides the color specified in first one if I use rect() and then fill() in both places (ie, both rects are green) but works as expected (ie, the first rect being blue and second being green) if I change the first rect() to fillRect(). Why is it so? I thought fillRect() was just rect() and then fill(), right?

ctx.translate(canvas.width/2, canvas.height/2);

ctx.fillStyle = "#5A9BDC";
ctx.fillRect(0, 0, rectWidth, rectHeight);
// ctx.rect(0, 0, rectWidth, rectHeight);
// ctx.fill();    

ctx.translate(-canvas.width/2, -canvas.height/2);

ctx.fillStyle = "#31B131";
ctx.rect(0, 0, rectWidth, rectHeight);
ctx.fill();

Tested in Chrome | Fiddle

Answer 1

fillRect

.fillRect is a "stand-alone" command that draws and fills a rectangle.

So if you issue multiple .fillRect commands with multiple .fillStyle commands, each new rect will be filled with the preceeding fillstyle.

ctx.fillStyle="red";
ctx.fillRect(10,10,10,10);  // filled with red

ctx.fillStyle="green";
ctx.fillRect(20,20,10,10);  // filled with green

ctx.fillStyle="blue";
ctx.fillRect(30,30,10,10);  // filled with blue

rect

.rect is part of the canvas's path commands.

Path commands are groups of drawings beginning with the beginPath() and continuing until another beginPath() is issued.

Within each group, only the last styling command wins.

So if you issue multiple .rect commands and multiple .fillStyle commands inside a path, only the last .fillStyle will be used on all the .rect's.

ctx.beginPath();  // path commands must begin with beginPath

ctx.fillStyle="red";
ctx.rect(10,10,10,10);  // blue

ctx.fillStyle="green";
ctx.rect(20,20,10,10);  // blue

ctx.fillStyle="blue";  // this is the last fillStyle, so it "wins"
ctx.rect(30,30,10,10);  // blue

// only 1 fillStyle is allowed per beginPath, so the last blue style fills all

ctx.fill()