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I wrote a little program to test how projected shadows work.
I wanted to check in particular the case where the point to project (it could be the vertex of a triangle) is not situated between the light source and the plane but behind the light itself, that is the light is between the point and the plane.
The problem is that my little program is not even working in the case where the point is between the light and plane. I checked the calculations tens of times, so I guess the error should be logic, but I cant find it..
Here the code
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;
}
}
If the plane is an xy plane, the light is on (0, 0, 10) and the point on (1, 0, 5) then the projected point on the plane should be (2, 0, 0), but the program is returning (400000.0, 0.0, 0.0, 1.0)..
Where am I wrong?
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