/usr/share/celestia/shaders/ringshadow.vp is in celestia-common 1.6.1+dfsg-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | !!VP1.0
# Vertex program used for applying ring shadow textures. Ray cast from a
# point on the object in the direction of the sun (assumed to be an
# infinitely distant light source here.) Compute the intersection of
# the ray with the ring plane. Then use the distance of the intersection
# point from the planet's center to compute a texture coordinate. Vertex
# programs are cool!
#
# c[0]..c[3] contains the concatenation of the modelview and projection
# matrices.
# c[16] contains the light direction in object space
# c[20] contains the color
# c[41] is [ inner ring radius, 1/ring width, 0, 0.5 ]
# c[42] is 1 / sunDir.y
# c[43] contains scaling vector [1 1-oblateness 1 0]
# Transform the vertex by the modelview matrix
DP4 o[HPOS].x, c[0], v[OPOS];
DP4 o[HPOS].y, c[1], v[OPOS];
DP4 o[HPOS].z, c[2], v[OPOS];
DP4 o[HPOS].w, c[3], v[OPOS];
# Scale by oblateness . . . off for now because it makes Saturn look
# weird, even though I think it's more realistic.
# MUL R2, v[OPOS], c[43];
MOV R2, v[OPOS];
MUL R1.x, R2.y, -c[42].x;
MAX R1.x, R1.x, c[42].w; # Clamp to zero--don't trace both directions
MAD R0, R1.x, c[16], R2;
# Compute the distance from the center. The s coordinate is the distance
# from the center, modified by the ring width and inner radius
DP3 R0.x, R0, R0;
RSQ R0.x, R0.x;
RCP R0.x, R0.x;
# Scale and bias by ring width and radius
ADD R0.x, R0.x, -c[41].x;
MUL R0.x, R0.x, c[41].y;
# Now we have our s coordinate . . .
MOV o[TEX0].x, R0.x;
# The t coordinate is always 0.5
MOV o[TEX0].y, c[41].w;
MOV o[COL0], c[20];
END
|