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Fix bugs in occlusion plane example code

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This commit is contained in:
Sauraen
2025-10-04 16:51:44 -07:00
parent 977a560c0a
commit 91a8528482
2 changed files with 9 additions and 30 deletions
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6
cpu/occlusionplane.c
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@@ -93,7 +93,7 @@ void ClipToScreenSpace(PlayState* play, const Vec3f* clipXYZ, float clipW, Vec2f
float preViewportY = clipXYZ->y * invW;
Vp* vp = &play->view.vp;
screen->x = (float)vp->vp.vscale[0] * preViewportX + (float)vp->vp.vtrans[0];
screen->y = -(float)vp->vp.vscale[1] * preViewportY + (float)vp->vp.vtrans[1];
screen->y = (float)vp->vp.vscale[1] * preViewportY + (float)vp->vp.vtrans[1];
}
bool ClipPolygon(PlayState* play, ClipVertex* verts, s8* indices, s8** idxFinalStart, s8** idxFinalEnd){
@@ -224,7 +224,7 @@ static OcclusionPlane sNoOcclusionPlane = {
0x0000,
0x0000,
0x0000,
0x8000
0x7FFF
};
OcclusionPlane* ComputeOcclusionPlane(PlayState* play, Vec3f* worldBounds){
@@ -248,7 +248,7 @@ OcclusionPlane* ComputeOcclusionPlane(PlayState* play, Vec3f* worldBounds){
s16 kx = FloatMinus1To1ToS16(kxf);
s16 ky = FloatMinus1To1ToS16(kyf);
s16 kz = FloatMinus1To1ToS16(kzf);
s16 kc = (s16)(kcf * 0.5f);
s16 kc = (s16)(kcf * -0.5f);
if((kx | ky | kz) == 0){
// Degenerate plane, disable the clipping
//sprintf(occPlaneMessage, "Clip space degenerate");

33
f3dex3.s
View File

@@ -344,37 +344,16 @@ ltBufOfs equ (lightBufferMain - altBase)
occlusionPlaneEdgeCoeffs:
/*
NOTE: This explanation is outdated; see cpu/occlusionplane.c
See cpu/occlusionplane.c for more information.
Vertex is in occlusion region if all five equations below are true:
4 * screenX[s13.2] * c0[s0.15] - 0.5 * screenY[s13.2] < c4[s14.1]
4 * screenY[s13.2] * c1[s0.15] - 0.5 * screenX[s13.2] < c5[s14.1]
4 * screenX[s13.2] * c2[s0.15] + 0.5 * screenY[s13.2] < c6[s14.1]
4 * screenY[s13.2] * c3[s0.15] + 0.5 * screenX[s13.2] < c7[s14.1]
clamp_to_0.s15(clipX[s15.16] * kx[0.s15])
+ clamp_to_0.s15(clipY[s15.16] * ky[0.s15])
+ clamp_to_0.s15(clipZ[s15.16] * kz[0.s15])
+ kc[0.s15]
>= 0
The first four can be rewritten as (again, vertex is occluded if all are true):
screenY > screenX * 8*c0 + -2*c4
screenX > screenY * 8*c1 + -2*c5
screenY < screenX * -8*c2 + 2*c6
screenX < screenY * -8*c3 + 2*c7
where screenX and screenY are in subpixels (e.g. screenX = 100 = 25.0 pixels),
c0-c3 are shorts representing -1:0.99997,
and c4-c7 are shorts representing "half pixels" (e.g. c4 = 50 = 25.0 pixels)
For the last equation, one option is to think of kx through kc as in s10.5 mode
instead, so a value of 0x0020 is 1.0 and they can range from -0x400.00 to
0x3FF.F8. This choice is because clipZ ranges from 0x0000.0000 at the camera
plane to 0x03FF.0000 at the maximum distance away. The normal distance Adult
Link is from the camera is about 0x00B0.0000.
A better option is to develop your plane equation in floating point, e.g.
clipX[f] * -0.2f + clipY[f] * 0.4f + clipZ[f] * 1.0f + -200.0f >= 0
then multiply everything by (32768.0f / max(abs(kx), abs(ky), abs(kz), abs(kc)))
(here 32768.0f / 200.0f = 163.84f)
clipX[f] * -32.77f + clipY[f] * 65.54f + clipZ[f] * 163.84f + -32768
clamp_to_0.s15(clipX[s15.16] * kx[s0.15])
+ clamp_to_0.s15(clipY[s15.16] * ky[s0.15])
+ clamp_to_0.s15(clipZ[s15.16] * kz[s0.15])
>= kc[s0.15]
*/
.dh 0x0000 // c0
.dh 0x0000 // c1
@@ -388,7 +367,7 @@ occlusionPlaneMidCoeffs:
.dh 0x0000 // kx
.dh 0x0000 // ky
.dh 0x0000 // kz
.dh 0x8000 // kc
.dh 0x7FFF // kc
// Alternate base address because vector load offsets can't reach all of DMEM.
// altBaseReg permanently points here.