CocosCreator Shader學習（三）：放大鏡縮小鏡效果

放大鏡縮小鏡效果

原理：根據縮放比例，判斷鏡面範圍內的點實際應該顯示哪個點的顏色值，問題就變成怎麼根據縮放比例進行座標轉換！

頂點着色器代碼不用修改。

片元着色器代碼如下：

CCProgram fs %{
  precision highp float;
  
  #include <alpha-test>

  in vec4 v_color;

  #if USE_TEXTURE
  in vec2 v_uv0;
  uniform sampler2D texture;
  #endif

  uniform inputData{
    float scale; //縮放比例 0~1~2
    float showRadius; //顯示半徑
    vec2 imageSize; //圖片實際尺寸
    vec2 point;  //縮放中心點
  };

  //檢查pos點是否在顯示圓內
  bool checkPointInCircle(vec2 pos){
    //pos是ndc座標，轉換成實際座標
    pos.x *= imageSize.x;
    pos.y = (1.0 - pos.y)*imageSize.y;

    //計算pos到point的距離
    float distance = sqrt(pow(pos.x - point.x, 2.0) + pow(pos.y - point.y, 2.0));
    return distance <= showRadius;
  }
  //根據縮放比例轉換座標
  vec2 getPointTransition(vec2 pos){
    vec2 uv = vec2(point.x/imageSize.x, 1.0 - point.y/imageSize.y);
    uv.x = uv.x - (uv.x - pos.x)/scale;
    uv.y = uv.y - (uv.y - pos.y)/scale;
    return uv;
  }

  void main () {
    vec4 o = vec4(1, 1, 1, 1);
    #if USE_TEXTURE
      if(checkPointInCircle(v_uv0)){
        vec2 uv = getPointTransition(v_uv0);
        if(uv.x > 1.0 || uv.x < 0.0 || uv.y > 1.0 || uv.y < 0.0){
          //超出紋理範圍的用黑色填充
          o = vec4(0, 0, 0, 1);
        }else{
          o *= texture(texture, uv);
          if(o.a == 0.0){
            //發現透明度爲0的座標，直接用黑色填充
            o = vec4(0, 0, 0, 1);
          }
        }
      }else{
        //不在圓內的點直接獲取紋理
        o *= texture(texture, v_uv0);
      }
      #if CC_USE_ALPHA_ATLAS_TEXTURE
      o.a *= texture2D(texture, v_uv0 + vec2(0, 0.5)).r;
      #endif
    #endif

    o *= v_color;

    ALPHA_TEST(o);

    gl_FragColor = o;
  }
}%

腳本代碼如下：

const {ccclass, property} = cc._decorator;

@ccclass
export default class Cocos3 extends cc.Component {

    @property(cc.Label)
    label: cc.Label = null;

    @property(cc.Slider)
    slider: cc.Slider = null;

    material: cc.Material = null;
    scale: number = 1.0;

    start () {
        this.material = this.node.getComponent(cc.Sprite).getMaterial(0);
        //設置初始縮放比例
        this.material.setProperty("scale", this.scale);
        //設置縮放顯示圓的半徑
        this.material.setProperty("showRadius", 50.0);
        //設置圖片寬高
        this.material.setProperty("imageSize", cc.v2(this.node.width, this.node.height));
        
        this.label.string = this.scale.toFixed(2);
        this.slider.progress = 0.5;
        this.slider.node.on("slide", this.sliderMoveCallBack, this);

        this.node.on(cc.Node.EventType.TOUCH_MOVE, this.touchMoveCallBack, this);
    }

    // update (dt) {}

    private sliderMoveCallBack(slider: cc.Slider)
    {
        this.scale = slider.progress*1.9 + 0.1;
        this.label.string = this.scale.toFixed(2);
        //修改縮放比例
        this.material.setProperty("scale", this.scale);
    }

    private touchMoveCallBack(event: cc.Event.EventTouch){
        //當前獲取到的觸摸點是相對於左下角爲原點的座標，
        //需要經過一系列換算成相對於當前精靈左下角爲原點的座標。
        let pos: cc.Vec2 = event.getLocation();
        pos = pos.sub(cc.v2(cc.winSize.width/2, cc.winSize.height/2));
        pos = pos.sub(this.node.getPosition());
        pos = pos.add(cc.v2(this.node.getContentSize().width/2, this.node.getContentSize().height/2));
        
        //修改縮放中心點
        this.material.setProperty("point", pos);
    }
}

效果圖如下：