src/main/java/eu/svjatoslav/sixth/e3d/renderer/raster/shapes/basic/texturedpolygon/PolygonBorderInterpolator.java

   1 /*
   2  * Sixth 3D engine. Author: Svjatoslav Agejenko.
   3  * This project is released under Creative Commons Zero (CC0) license.
   4  */
   5 package eu.svjatoslav.sixth.e3d.renderer.raster.shapes.basic.texturedpolygon;
   6
   7 import eu.svjatoslav.sixth.e3d.geometry.Point2D;
   8
   9 import static java.lang.Math.abs;
  10
  11 /**
  12  * Interpolator for textured polygon edges with perspective correction.
  13  * <p>
  14  * This class maps screen coordinates to texture coordinates while maintaining
  15  * perspective accuracy.
  16  * It's used to create texture-mapped scanlines that adjust for depth (z) to
  17  * prevent texture distortion.
  18  * <p>
  19  * The comparison logic ensures proper scanline ordering based on vertical
  20  * coverage and horizontal span.
  21  */
  22 public class PolygonBorderInterpolator implements
  23         Comparable<PolygonBorderInterpolator> {
  24
  25     // on-screen coordinates
  26     Point2D onScreenPoint1;
  27     Point2D onScreenPoint2;
  28
  29     double distanceFromY1;
  30     private int onScreenHeight;
  31     private int onScreenWidth;
  32     private int onscreenAbsoluteHeight;
  33     private double textureWidth;
  34     private double textureHeight;
  35     // texture coordinates
  36     private Point2D texturePoint1;
  37     private Point2D texturePoint2;
  38
  39
  40     @Override
  41     public boolean equals(final Object o) {
  42         if (o == null) return false;
  43
  44         return o instanceof PolygonBorderInterpolator && compareTo((PolygonBorderInterpolator) o) == 0;
  45     }
  46
  47     @Override
  48     public int hashCode() {
  49         int result = onScreenWidth;
  50         result = 31 * result + onscreenAbsoluteHeight;
  51         return result;
  52     }
  53
  54     @Override
  55     public int compareTo(final PolygonBorderInterpolator otherInterpolator) {
  56         if (onscreenAbsoluteHeight < otherInterpolator.onscreenAbsoluteHeight)
  57             return 1;
  58         if (onscreenAbsoluteHeight > otherInterpolator.onscreenAbsoluteHeight)
  59             return -1;
  60
  61         if (onScreenWidth < otherInterpolator.onScreenWidth)
  62             return 1;
  63         if (onScreenWidth > otherInterpolator.onScreenWidth)
  64             return -1;
  65
  66         return 0;
  67     }
  68
  69     public boolean containsY(final int y) {
  70
  71         if (onScreenPoint1.y < onScreenPoint2.y) {
  72             if (y >= onScreenPoint1.y)
  73                 return y <= onScreenPoint2.y;
  74         } else if (y >= onScreenPoint2.y)
  75             return y <= onScreenPoint1.y;
  76
  77         return false;
  78     }
  79
  80     public double getTX() {
  81
  82         if (onScreenHeight == 0)
  83             return (texturePoint2.x + texturePoint1.x) / 2d;
  84
  85         return texturePoint1.x + ((textureWidth * distanceFromY1) / onScreenHeight);
  86     }
  87
  88     public double getTY() {
  89
  90         if (onScreenHeight == 0)
  91             return (texturePoint2.y + texturePoint1.y) / 2d;
  92
  93         return texturePoint1.y + ((textureHeight * distanceFromY1) / onScreenHeight);
  94     }
  95
  96     public int getX() {
  97
  98         if (onScreenHeight == 0)
  99             return (int) ((onScreenPoint2.x + onScreenPoint1.x) / 2d);
 100
 101         return (int) (onScreenPoint1.x + ((onScreenWidth * distanceFromY1) / onScreenHeight));
 102     }
 103
 104     public void setCurrentY(final int y) {
 105         distanceFromY1 = y - onScreenPoint1.y;
 106     }
 107
 108     public void setPoints(final Point2D onScreenPoint1, final Point2D onScreenPoint2,
 109                           final Point2D texturePoint1, final Point2D texturePoint2) {
 110
 111         this.onScreenPoint1 = onScreenPoint1;
 112         this.onScreenPoint2 = onScreenPoint2;
 113         this.texturePoint1 = texturePoint1;
 114         this.texturePoint2 = texturePoint2;
 115
 116         onScreenHeight = (int) (onScreenPoint2.y - onScreenPoint1.y);
 117         onScreenWidth = (int) (onScreenPoint2.x - onScreenPoint1.x);
 118         onscreenAbsoluteHeight = abs(onScreenHeight);
 119
 120         textureWidth = texturePoint2.x - texturePoint1.x;
 121         textureHeight = texturePoint2.y - texturePoint1.y;
 122     }
 123
 124 }