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      1 package com.jme3.scene.mesh;
      2 
      3 import com.jme3.scene.Mesh.Mode;
      4 import java.nio.Buffer;
      5 
      6 /**
      7  * IndexBuffer implementation that generates vertex indices sequentially
      8  * based on a specific Mesh {@link Mode}.
      9  * The generated indices are as if the mesh is in the given mode
     10  * but contains no index buffer, thus this implementation will
     11  * return the indices if the index buffer was there and contained sequential
     12  * triangles.
     13  * Example:
     14  * <ul>
     15  * <li>{@link Mode#Triangles}: 0, 1, 2 | 3, 4, 5 | 6, 7, 8 | ...</li>
     16  * <li>{@link Mode#TriangleStrip}: 0, 1, 2 | 2, 1, 3 | 2, 3, 4 | ...</li>
     17  * <li>{@link Mode#TriangleFan}: 0, 1, 2 | 0, 2, 3 | 0, 3, 4 | ...</li>
     18  * </ul>
     19  *
     20  * @author Kirill Vainer
     21  */
     22 public class VirtualIndexBuffer extends IndexBuffer {
     23 
     24     protected int numVerts = 0;
     25     protected int numIndices = 0;
     26     protected Mode meshMode;
     27 
     28     public VirtualIndexBuffer(int numVerts, Mode meshMode){
     29         this.numVerts = numVerts;
     30         this.meshMode = meshMode;
     31         switch (meshMode) {
     32             case Points:
     33                 numIndices = numVerts;
     34                 return;
     35             case LineLoop:
     36                 numIndices = (numVerts - 1) * 2 + 1;
     37                 return;
     38             case LineStrip:
     39                 numIndices = (numVerts - 1) * 2;
     40                 return;
     41             case Lines:
     42                 numIndices = numVerts;
     43                 return;
     44             case TriangleFan:
     45                 numIndices = (numVerts - 2) * 3;
     46                 return;
     47             case TriangleStrip:
     48                 numIndices = (numVerts - 2) * 3;
     49                 return;
     50             case Triangles:
     51                 numIndices = numVerts;
     52                 return;
     53             case Hybrid:
     54                 throw new UnsupportedOperationException();
     55         }
     56     }
     57 
     58     @Override
     59     public int get(int i) {
     60         if (meshMode == Mode.Triangles || meshMode == Mode.Lines || meshMode == Mode.Points){
     61             return i;
     62         }else if (meshMode == Mode.LineStrip){
     63             return (i + 1) / 2;
     64         }else if (meshMode == Mode.LineLoop){
     65             return (i == (numVerts-1)) ? 0 : ((i + 1) / 2);
     66         }else if (meshMode == Mode.TriangleStrip){
     67            int triIndex   = i/3;
     68            int vertIndex  = i%3;
     69            boolean isBack = (i/3)%2==1;
     70            if (!isBack){
     71                 return triIndex + vertIndex;
     72            }else{
     73                switch (vertIndex){
     74                    case 0: return triIndex + 1;
     75                    case 1: return triIndex;
     76                    case 2: return triIndex + 2;
     77                    default: throw new AssertionError();
     78                }
     79             }
     80         }else if (meshMode == Mode.TriangleFan){
     81             int vertIndex = i%3;
     82             if (vertIndex == 0)
     83                 return 0;
     84             else
     85                 return (i / 3) + vertIndex;
     86         }else{
     87             throw new UnsupportedOperationException();
     88         }
     89     }
     90 
     91     @Override
     92     public void put(int i, int value) {
     93         throw new UnsupportedOperationException("Does not represent index buffer");
     94     }
     95 
     96     @Override
     97     public int size() {
     98         return numIndices;
     99     }
    100 
    101     @Override
    102     public Buffer getBuffer() {
    103         return null;
    104     }
    105 
    106 }
    107