Release v5.5.0 - #41

A sprite with rotation style LEFT_RIGHT that faces left now has its hitbox
mirrored along with its costume. The costume was drawn flipped but the hitbox
was not, so a costume whose painted part is not in the middle of its canvas
collided with the empty side - and a hitbox set with setHitbox to cover, say,
only the front of a sprite stayed at its back after it turned around. Speech
and thought bubbles follow the mirrored costume as well. The Online IDE already
mirrored the hitbox.

Sprites can sense colours, like Scratch's touching color? and
color is touching color? blocks:

if (this.isTouchingColor(HtmlColor.RED)) { ... }
if (this.isTouchingColor(255, 0, 0)) { ... }
if (this.isColorTouchingColor(HtmlColor.YELLOW, HtmlColor.BLUE)) { ... }

A sprite touches a colour when anything it paints lies over that colour on the
stage: on the backdrop, on what the pen drew, or on another sprite. Nearly
equal colours count, with the same tolerance as Scratch, so anti-aliased edges
still match. The check only looks at the pixels the sprite covers, so it costs
the same on a 480 x 360 stage as on a 1920 x 1080 one; a 128 x 128 sprite takes
well under a millisecond.

A sprite can turn around a point of its own choosing, like Scratch's rotation
center:

this.setRotationCenter(54, 239); // in the costume's pixels, from its top left corner

The point sits at the sprite's position, the costume turns and mirrors around
it, and the hitbox, stamps, speech bubbles and colour sensing follow. It is
given like the points of setHitbox, grows with the sprite's size and holds
for every costume. Without it, a sprite turns around the middle of its costume
as before.

getShaders().add(name, fragmentShaderPath, null) works. Leaving out the
vertex shader is what the documentation shows, but it stopped the program with
a NullPointerException; Processing's default vertex shader is now used.

Every built-in sprite with a front now faces right, the way a sprite with
direction 90 faces in Scratch. The ships, lasers and other parts of the space
shooter sheet were drawn pointing up (the enemies down), and the bee, fly,
fishes, frog, ladybug, mouse, slimes, snail and worms of the platformer sheet
facing left. So a slime walking right with move walked backwards, and a ship
told to pointTowardsMousePointer pointed its side at the mouse. They are now
turned when they are loaded. A program that showed a ship pointing up at
direction 90 now shows it pointing right; setDirection(0) points it up, and
then move flies it up as well.

A broadcast now reaches every sprite on the stage and the stage itself, as in
Scratch and in the Online IDE. Sprite.broadcast left out the sprite that sent
it, and Stage.broadcast left out the stage, so a sprite or stage that reacts
to its own message in whenIReceive never heard it. A sprite that broadcasts
the same message from its own whenIReceive now calls itself again, as the
same script does in Scratch.