BabylonJS - 貼花

貼花就像貼在物體上的貼紙。貼紙圖案是藉助繪製在網格上的二維影像完成的（例如，遊戲中的物體）。在遊戲中，假設你有一支軍隊在發射子彈，需要在物體上看到子彈的印記。所以在 BabylonJS 中，這是使用貼花來完成的，當你點選任何物體時，你將在點選的位置繪製一個二維影像。

貼花用於在建立的網格上新增細節——例如子彈、孔洞等細節。在下面給出的演示連結中，我們使用一個影像並將其新增到匯入的網格中。

要新增貼花，您可以使用以下程式碼：

var newDecal = BABYLON.Mesh.CreateDecal("decal", mesh, decalPosition, normal, decalSize, angle);

執行以下程式碼以在網格上新增貼花：

BABYLON.SceneLoader.ImportMesh("Shcroendiger'scat", "scenes/", "SSAOcat.babylon", scene, function (newMeshes) {
   var cat = newMeshes[0]; / /this is mesh shown on the screen.

   // Set the target of the camera to the first imported mesh
   camera.target = cat;

   var decalMaterial = new BABYLON.StandardMaterial("decalMat", scene);
   decalMaterial.diffuseTexture = new BABYLON.Texture("images/impact1.jpg", scene);
   decalMaterial.diffuseTexture.hasAlpha = true;
   decalMaterial.zOffset = -2;

   var onPointerDown = function (evt) {
      if (evt.button !== 0) {
         return;
      }

      // check if we are under a mesh
      var pickInfo = scene.pick(scene.pointerX, scene.pointerY, function (mesh) { return mesh === cat; 
      // this will give all the meshes , but it will pick the mesh whch is same as cat and return true if it is found });
      if (pickInfo.hit) { // if true
         var decalSize = new BABYLON.Vector3(5, 5, 5); //size of decal is defined

         var newDecal = BABYLON.Mesh.CreateDecal("decal", cat, pickInfo.pickedPoint, pickInfo.getNormal(true), decalSize); //decal is created 
         newDecal.material = decalMaterial; //decal material is added.
      }
   }
   var canvas = engine.getRenderingCanvas();
   canvas.addEventListener("pointerdown", onPointerDown, false);

   scene.onDispose = function () {
      canvas.removeEventListener("pointerdown", onPointerDown);
   }
});

演示

<!doctype html>
<html>
   <head>
      <meta charset = "utf-8">
      <title>BabylonJs - Basic Element-Creating Scene</title>
      <script src = "babylon.js"></script>
      <style>
         canvas {width: 100%; height: 100%;}
      </style>
   </head>

   <body>
      <canvas id = "renderCanvas"></canvas>
      <script type = "text/javascript">
         var canvas = document.getElementById("renderCanvas");
         var engine = new BABYLON.Engine(canvas, true);
         
         var createScene  = function() {
            var scene = new BABYLON.Scene(engine);

            //Adding a light
            var light = new BABYLON.HemisphericLight("Hemi", new BABYLON.Vector3(0, 1, 0), scene);

            //Adding an Arc Rotate Camera
            var camera = new BABYLON.ArcRotateCamera("Camera", -1.85, 1.2, 200, BABYLON.Vector3.Zero(), scene);

            camera.attachControl(canvas, true);

            // The first parameter can be used to specify which mesh to import. Here we import all meshes
            BABYLON.SceneLoader.ImportMesh("Shcroendiger'scat", "scenes/", "SSAOcat.babylon", scene, function (newMeshes) {
               var cat = newMeshes[0];

               // Set the target of the camera to the first imported mesh
               camera.target = cat;

               var decalMaterial = new BABYLON.StandardMaterial("decalMat", scene);
               decalMaterial.diffuseTexture = new BABYLON.Texture("images/impact1.jpg", scene);
               decalMaterial.diffuseTexture.hasAlpha = true;
               decalMaterial.zOffset = -2;

               var onPointerDown = function (evt) {
                  if (evt.button !== 0) {
                     return;
                  }

                  // check if we are under a mesh
                  var pickInfo = scene.pick(scene.pointerX, scene.pointerY, function (mesh) { return mesh === cat; });
                  if (pickInfo.hit) {
                     var decalSize = new BABYLON.Vector3(5, 5, 5);

                     var newDecal = BABYLON.Mesh.CreateDecal("decal", cat, pickInfo.pickedPoint, pickInfo.getNormal(true), decalSize);
                     newDecal.material = decalMaterial;
                  }
               }
               var canvas = engine.getRenderingCanvas();
               canvas.addEventListener("pointerdown", onPointerDown, false);

               scene.onDispose = function () {
                  canvas.removeEventListener("pointerdown", onPointerDown);
               }
            });	
            return scene;
         };
         var scene = createScene();
         engine.runRenderLoop(function() {
            scene.render();
         });
      </script>
   </body>
</html>

在上面的演示連結中，我們使用了 SSAOcat.babylon 網格。您可以從此處下載 SSAOcat.babylon 的 json 檔案：

SSAOcat.babylon

將檔案儲存在 scenes/ 資料夾中。這將幫助您獲得如下所示的輸出。

輸出

以上程式碼行生成以下輸出：

在這個演示中，我們使用了影像 **impact1.jpg**。這些影像儲存在本地 images/ 資料夾中，並也在下面貼上供參考。您可以下載任何您選擇的影像並在演示連結中使用。

images/impact1.jpg

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