Cocos2d-x屏幕适配
资源分辨率，设计分辨率，屏幕分辨率
- Resources width 以下简写为RW，Resources height 以下简写为RH
- Design width 以下简写为DW，Design height 以下简写为DH
- Screen width 以下简写为SW，Screen height 以下简写为SH
接口setContentScaleFactor()和setSearchPaths()控制着第一个转换过程。
而setDesignResolutionSize()控制第二个过程。两个过程结合在一起，影响最终的显示效果。
从资源分辨率到设计分辨率
setSearchPaths()需要根据当前屏幕分辨率做恰当的设置。
setContentScaleFactor()决定了图片显示到屏幕的缩放因子，但是这个接口的参数不是通过资源图片的宽、高比屏幕宽、高得来。Cocos2d-x引擎设计试图屏蔽游戏开发者直接去关注屏幕，所以这个因子是资源宽、高比设计分辨率宽、高。
setContentScaleFactor()通常有两个方式来设置参数。 RH/DH或RW/DW，不同的因子选择有不同的缩放负作用。 先看一张图:
用高度比作为内容缩放因子，保证了背景资源的垂直方向在设计分辨率范围内的全部显示。
用宽度比作为内容缩放因子，保证了背景资源的水平方向在设计分辨率范围内的全部显示。
从设计分辨率到屏幕分辨率
首先，我们通过一张图了解下Cocos2d-X的几种屏幕适配规则：
1. EXACT_FIT将设计尺寸映射到屏幕尺寸，长宽按各自比例拉伸，可能造成图像拉伸变形。
2. SHOW_ALL和NO_BORDER都是长宽等比例拉伸，图像不会被拉伸变形；但可能造成黑边和资源显示不全的问题。
3. FIXED_HEIGHT和FIXED_WIDTH和之前的三种策略不同，EXACT_FIT、SHOW_ALL和NO_BORDER都不会修正设计尺寸，而FIXED_HEIGHT和FIXED_WIDTH在设计阶段就修正设计尺寸，让可视区域就是设计尺寸区域。
4. NO_BORDER是唯一可视区域小于最终设计区域（FIXED_HEIGHT和FIXED_WIDTH会修正传入的设计尺寸）的一种策略。其他几种策略的设计区域等于设计区域。
5. NO_BORDER、FIXED_HEIGHT和FIXED_WIDTH三种策略根据设计或可视区域的改变需要做相应的坐标适配。
FIXED_HEIGHT:
1. 如果屏幕尺寸长高比>资源尺寸长高比，进行坐标偏差纠正，让资源居中显示，左右两边留黑边。
2. 如果屏幕尺寸长高比<资源尺寸长高比，进行坐标偏差纠正，让资源居中显示，左右两边被裁剪无法显示。
所以，屏幕尺寸长高比略小于资源尺寸长高比，显示效果最佳。
源码面前无秘密
class CC_DLL GLView : public Ref
{
/** * Get the frame size of EGL view. * In general,it returns the screen size since the EGL view is a fullscreen view. * * @return The frame size of EGL view. */
const Size& GLView::getFrameSize() const
{
return _screenSize;
}
/** * Set the frame size of EGL view. * * @param width The width of the fram size. * @param height The height of the fram size. */
void GLView::setFrameSize(float width,float height)
{
_screenSize = Size(width,height);
}
/** * Get the visible area size of opengl viewport. * * @return The visible area size of opengl viewport. */
Size GLView::getVisibleSize() const
{
if (_resolutionPolicy == ResolutionPolicy::NO_BORDER)
{
return Size(_screenSize.width/_scaleX,_screenSize.height/_scaleY);
}
else
{
return _designResolutionSize;
}
}
/** * Get the visible origin point of opengl viewport. * * @return The visible origin point of opengl viewport. */
Vec2 GLView::getVisibleOrigin() const
{
if (_resolutionPolicy == ResolutionPolicy::NO_BORDER)
{
return Vec2((_designResolutionSize.width - _screenSize.width/_scaleX)/2,(_designResolutionSize.height - _screenSize.height/_scaleY)/2);
}
else
{
return Vec2::ZERO;
}
}
/** * Set the design resolution size. * @param width Design resolution width. * @param height Design resolution height. * @param resolutionPolicy The resolution policy desired,you may choose: * [1] EXACT_FIT Fill screen by stretch-to-fit: if the design resolution ratio of width to height is different from the screen resolution ratio,your game view will be stretched. * [2] NO_BORDER Full screen without black border: if the design resolution ratio of width to height is different from the screen resolution ratio,two areas of your game view will be cut. * [3] SHOW_ALL Full screen with black border: if the design resolution ratio of width to height is different from the screen resolution ratio,two black borders will be shown. */
void GLView::setDesignResolutionSize(float width,float height,ResolutionPolicy resolutionPolicy)
{
CCASSERT(resolutionPolicy != ResolutionPolicy::UNKNOWN,"should set resolutionPolicy");
if (width == 0.0f || height == 0.0f)
{
return;
}
_designResolutionSize.setSize(width,height);
_resolutionPolicy = resolutionPolicy;
updateDesignResolutionSize();
}
void GLView::updateDesignResolutionSize()
{
if (_screenSize.width > 0 && _screenSize.height > 0
&& _designResolutionSize.width > 0 && _designResolutionSize.height > 0)
{
_scaleX = (float)_screenSize.width / _designResolutionSize.width;
_scaleY = (float)_screenSize.height / _designResolutionSize.height;
if (_resolutionPolicy == ResolutionPolicy::NO_BORDER)
{
_scaleX = _scaleY = MAX(_scaleX,_scaleY);
}
else if (_resolutionPolicy == ResolutionPolicy::SHOW_ALL)
{
_scaleX = _scaleY = MIN(_scaleX,_scaleY);
}
else if ( _resolutionPolicy == ResolutionPolicy::FIXED_HEIGHT) {
_scaleX = _scaleY;
_designResolutionSize.width = ceilf(_screenSize.width/_scaleX);
}
else if ( _resolutionPolicy == ResolutionPolicy::FIXED_WIDTH) {
_scaleY = _scaleX;
_designResolutionSize.height = ceilf(_screenSize.height/_scaleY);
}
// calculate the rect of viewport
float viewPortW = _designResolutionSize.width * _scaleX;
float viewPortH = _designResolutionSize.height * _scaleY;
_viewPortRect.setRect((_screenSize.width - viewPortW) / 2,(_screenSize.height - viewPortH) / 2,viewPortW,viewPortH);
// reset director's member variables to fit visible rect
auto director = Director::getInstance();
director->_winSizeInPoints = getDesignResolutionSize();
director->_isStatusLabelUpdated = true;
director->setProjection(director->getProjection());
// Github issue #16139
// A default viewport is needed in order to display the FPS,
// since the FPS are rendered in the Director,and there is no viewport there.
// Everything,including the FPS should renderer in the Scene.
glViewport(0,0,_screenSize.width,_screenSize.height);
}
}
}；
设置/获取屏幕的大小（主要是desktop系统上设置，也用于调试各屏幕适配的情况是否符合我们的预期等）：
void GLView:: setFrameSize(float width,float height)
const Size& GLView::getFrameSize() const设置/获取设计尺寸大小（相当于我们设定了我们的创作区域大小、最终如何显示到屏幕上，通过ResolutionPolicy指定。
注意：SHOW_ALL、EXACT_FIT、NO_BORDER三种策略的设计分辨率都是传入值，内部不做修正。FIXED_HEIGHT和FIXED_WIDTH都是会在内部修正传入设计分辨率，以保证屏幕分辨率到设计分辨率无拉伸铺满屏幕，所以通过getDesignResolutionSize()获取的值可能与传入的值不一致。
void GLView:: setDesignResolutionSize(float width,float height,ResolutionPolicy resolutionPolicy)
const Size& GLView::getDesignResolutionSize() const获取可视区域的大小和原点,即我们设定的setDesignResolutionSize大小有多少是可以被显示的。由于适配策略NO_BORDER，有可能设计区域有部分最终无法在屏幕上显示，所以这里需要计算，可视原点也可能不是(0，0)。还有由于我们通过setDesignResolutionSize设置的设计尺寸大小，FIXED_HEIGHT、FIXED_WIDTH因为需要裁剪，所以这里的可视区域大小也是经过裁剪后的大小。
Size GLView::getVisibleSize() const
Vec2 Director::getVisibleOrigin() const这里获取的WinSize，即setDesignResolutionSize设置后经过计算裁剪（可能）的_designResolutionSize。 const Size& Director::getWinSize(void) const
