Support for fixed sprite content size regardless of new texture content

[rh101]

• axmol version: https://github.com/axmolengine/axmol/tree/1baf5cde3b0ccadf63fef045521723497d6f346f

This isn't really a bug, since the current implementation is correct. Sprite frames can have different sizes, and a sprite should change size depending on the texture size of the frame.

It would be nice to have the ability to lock the sprite size so that it ignores the new frame texture size. This would typically be used with stretch mode enabled.

Use grossini.plist sprite sheet and texture from cpp-tests.

auto spriteCache = SpriteFrameCache::getInstance();
spriteCache->addSpriteFramesWithFile("grossini.plist");

ax::Vector<ax::SpriteFrame*> animFrames;
for (int i = 1; i < 15; i++)
{
    auto frameName = fmt::format("grossini_dance_{:02}.png", i);
    animFrames.pushBack(spriteCache->getSpriteFrameByName(frameName));
}

auto* animation = ax::Animation::createWithSpriteFrames(animFrames, 1 / 25.f, -1);
auto* animationAction = ax::Animate::create(animation);
auto animatingSprite  = ax::Sprite::createWithSpriteFrame(animFrames.front());
animatingSprite->setPosition(visibleSize / 2);
animatingSprite->setStretchEnabled(true);
animatingSprite->setContentSize(ax::Vec2(200, 200));
animatingSprite->runAction(animationAction);
this->addChild(animatingSprite);

Expected output when animating (size of 200, 200 due to stretch factor):

Actual output while animating:

[rh101]

Not sure about the best way to add this feature.

Can add a new FixedSizeAnimate action is added that always sets the same content size after each new frame on a sprite, but that means calculations inside the Sprite will be done twice, once in the chain called from setSpriteFrame -> setTextyureRect etc., and then another by the extra setContentSize. They all end up calling updateStretchFactor(); and updatePoly();, so they'll be called twice for every frame.

Another option would be to add something to Sprite to indicate that the content size is fixed, and should not change on new textures/frames (as long as it's not a content size of 0, 0).

[rh101]

With PR #1897 a simple call to sprite->setContentSizeDynamic(false); sprite->setAutoSize(false); would enable the functionality described above.

[halx99]

API: change to setAutoSize?

[rh101]

API: change to setAutoSize?

Yes! That makes way more sense. Will update the PR.