我写了一个小程序来测试投影阴影是如何工作的。
我想特别检查投影点（可能是三角形的顶点）不位于光源和平面之间而是位于光本身后面的情况，即光位于点和平面之间.
问题是我的小程序甚至在点位于光和平面之间的情况下都不起作用。我检查了数十次计算，所以我猜应该是逻辑错误，但我找不到它..
这里的代码
public class test {
int x = 0;
int y = 1;
int z = 2;
int w = 3;
float floor[][] = {
{-100.0f, -100.0f, 0.0f},
{100.0f, -100.0f, 0.0f},
{100.0f, 100.0f, 0.0f},
{-100.0f, 100.0f, 0.0f}};
private float shadow_floor[] = new float[16];
float light_position[] = {0.0f, 0.0f, 10.0f, 1.0f};
public test() {
//Find floorplane based on thre known points
float plane_floor[] = calculatePlane(floor[1], floor[2], floor[3]);
//store shadowMatrix for floor
shadow_floor = shadowMatrix(plane_floor, light_position);
float[] point = new float[]{1.0f, 0.0f, 5.0f, 1.0f};
float[] projectedPoint = pointFmatrixF(point, shadow_floor);
System.out.println("point: (" + point[x] + ", " + point[y] + ", " + point[z] + ", "
+ point[w] + ")");
System.out.println("projectedPoint: (" + projectedPoint[x] + ", " + projectedPoint[y]
+ ", " + projectedPoint[z] + ", " + projectedPoint[w] + ")");
}
public static void main(String args[]) {
test test = new test();
}
// make shadow matrix
public float[] shadowMatrix(float plane[], float light_pos[]) {
float shadow_mat[] = new float[16];
float dot;
dot = plane[x] * light_pos[x] + plane[y] * light_pos[y]
+ plane[z] * light_pos[z] + plane[w] * light_pos[w];
shadow_mat[0] = dot - light_pos[x] * plane[x];
shadow_mat[4] = -light_pos[x] * plane[y];
shadow_mat[8] = -light_pos[x] * plane[z];
shadow_mat[12] = -light_pos[x] * plane[3];
shadow_mat[1] = -light_pos[y] * plane[x];
shadow_mat[5] = dot - light_pos[y] * plane[y];
shadow_mat[9] = -light_pos[y] * plane[z];
shadow_mat[13] = -light_pos[y] * plane[w];
shadow_mat[2] = -light_pos[z] * plane[x];
shadow_mat[6] = -light_pos[z] * plane[y];
shadow_mat[10] = dot - light_pos[z] * plane[z];
shadow_mat[14] = -light_pos[z] * plane[w];
shadow_mat[3] = -light_pos[w] * plane[x];
shadow_mat[7] = -light_pos[w] * plane[y];
shadow_mat[11] = -light_pos[w] * plane[z];
shadow_mat[15] = dot - light_pos[w] * plane[w];
return shadow_mat;
}
public float[] calculatePlane(float p1[], float p2[], float p3[]) {
//Array for planlikningen
float plane[] = new float[4];
//Gitt to vektorer (tre punkter) i planet kan normalen regnes ut
//Vi vil ha aboluttverdier
plane[x] = Math.abs(((p2[y] - p1[y]) * (p3[z] - p1[z])) - ((p2[z] - p1[z])
* (p3[y] - p1[y])));
plane[y] = Math.abs(((p2[z] - p1[z]) * (p3[x] - p1[x])) - ((p2[x] - p1[x])
* (p3[z] - p1[z])));
plane[z] = Math.abs(((p2[x] - p1[x]) * (p3[y] - p1[y])) - ((p2[y] - p1[y])
* (p3[x] - p1[x])));
plane[w] = -(plane[x] * p1[x] + plane[y] * p1[y] + plane[z] * p1[z]);
return plane;
}
public float[] pointFmatrixF(float[] point, float[] matrix) {
int x = 0;
int y = 1;
int z = 2;
float[] transformedPoint = new float[4];
transformedPoint[x] =
matrix[0] * point[x]
+ matrix[4] * point[y]
+ matrix[8] * point[z]
+ matrix[12];
transformedPoint[y] =
matrix[1] * point[x]
+ matrix[5] * point[y]
+ matrix[9] * point[z]
+ matrix[13];
transformedPoint[z] =
matrix[2] * point[x]
+ matrix[6] * point[y]
+ matrix[10] * point[z]
+ matrix[14];
transformedPoint[w] = 1;
return transformedPoint;
}
}
如果平面是 xy 平面，灯光在 (0, 0, 10) 并且点在 (1, 0, 5) 上，那么平面上的投影点应该是 (2, 0, 0)，但是程序正在返回 (400000.0, 0.0, 0.0, 1.0)