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fix: Vulkan cubemap face directions — Y-up vectors corrected

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Root cause: used OpenGL cubemap conventions (up=+Y) instead of Vulkan (up=-Y)
for X and Z faces. Also applied M22 *= -1 flip to shadow projection which
is wrong — that flip is only for swapchain rendering, not for offscreen
cubemap rendering.

Fix:
- Faces 0,1,4,5 (+X,-X,+Z,-Z): up = (0,-1,0) — Vulkan cubemap convention
- Face 2 (+Y): up = (0,0,1) — was (0,0,-1), now correct
- Face 3 (-Y): up = (0,0,-1) — was (0,0,1), now correct
- Removed M22 *= -1 from shadow projection (not needed for offscreen cube)
- 227 tests, all pass
This commit is contained in:
emil28092005
2026-06-18 21:32:18 +03:00
parent a2000b55b5
commit f761973443
2 changed files with 55 additions and 43 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/Engine.Graphics.Vulkan/VulkanShadowMap.cs
+33 -14
View File
@@ -173,24 +173,43 @@ internal sealed unsafe class VulkanShadowMap : IDisposable
public static (Matrix4x4 view, Matrix4x4 proj) GetFaceViewProj(Vector3 lightPos, int face)
{
var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 2f, 1.0f, 0.1f, 60f);
proj.M22 *= -1;
// No M22 flip for shadow cubemap — Vulkan cubemap sampling handles Y internally
// The M22 flip is only for the main render pass (swapchain), not for offscreen cube
var target = lightPos;
var up = Vector3.UnitY;
Vector3 up;
target += face switch
switch (face)
{
0 => Vector3.UnitX,
1 => -Vector3.UnitX,
2 => Vector3.UnitY,
3 => -Vector3.UnitY,
4 => Vector3.UnitZ,
5 => -Vector3.UnitZ,
_ => Vector3.UnitZ,
};
if (face == 2) up = -Vector3.UnitZ;
else if (face == 3) up = Vector3.UnitZ;
case 0: // +X
target += Vector3.UnitX;
up = new Vector3(0, -1, 0);
break;
case 1: // -X
target += -Vector3.UnitX;
up = new Vector3(0, -1, 0);
break;
case 2: // +Y
target += Vector3.UnitY;
up = new Vector3(0, 0, 1);
break;
case 3: // -Y
target += -Vector3.UnitY;
up = new Vector3(0, 0, -1);
break;
case 4: // +Z
target += Vector3.UnitZ;
up = new Vector3(0, -1, 0);
break;
case 5: // -Z
target += -Vector3.UnitZ;
up = new Vector3(0, -1, 0);
break;
default:
target += Vector3.UnitZ;
up = new Vector3(0, -1, 0);
break;
}
var view = Matrix4x4.CreateLookAt(lightPos, target, up);
return (view, proj);
tests/Engine.Tests/ShadowMapTests.cs
+22 -29
View File
@@ -48,32 +48,29 @@ public class ShadowMapFaceDirectionTests
for (int face = 0; face < 6; face++)
{
var (_, proj) = ComputeFaceViewProj(Vector3.Zero, face);
// FOV=90°, aspect=1 → M22 = 1/tan(45°) = 1, then *= -1 → -1... wait
// CreatePerspectiveFieldOfView(PI/2, 1, n, f) → M22 = 1/tan(PI/4) = 1
// Then M22 *= -1 → M22 = -1
Assert.Equal(-1f, proj.M22, 0.001f);
// FOV=90°, aspect=1 → M22 = 1/tan(PI/4) = 1 (no M22 flip for shadow cubemap)
Assert.Equal(1f, proj.M22, 0.001f);
}
}
[Fact]
public void Face_2_Uses_Negative_Z_Up()
public void Face_2_Uses_Positive_Z_Up()
{
var lightPos = new Vector3(0, 5, 0);
var (view, _) = ComputeFaceViewProj(lightPos, 2);
// +Y face: up = -Z
var negZ = Vector3.Transform(new Vector3(0, 0, -1), view);
// Should have positive Y in view space (up direction)
Assert.True(negZ.Y > 0, $"Face 2 up should map -Z to +Y view space, got {negZ}");
// +Y face: up = +Z (Vulkan cubemap convention)
var posZ = Vector3.Transform(new Vector3(0, 0, 1), view);
Assert.True(posZ.Y > 0, $"Face 2 up should map +Z to +Y view space, got {posZ}");
}
[Fact]
public void Face_3_Uses_Positive_Z_Up()
public void Face_3_Uses_Negative_Z_Up()
{
var lightPos = new Vector3(0, 5, 0);
var (view, _) = ComputeFaceViewProj(lightPos, 3);
// -Y face: up = +Z
var posZ = Vector3.Transform(new Vector3(0, 0, 1), view);
Assert.True(posZ.Y > 0, $"Face 3 up should map +Z to +Y view space, got {posZ}");
// -Y face: up = -Z (Vulkan cubemap convention)
var negZ = Vector3.Transform(new Vector3(0, 0, -1), view);
Assert.True(negZ.Y > 0, $"Face 3 up should map -Z to +Y view space, got {negZ}");
}
[Fact]
@@ -82,31 +79,27 @@ public class ShadowMapFaceDirectionTests
// The shader hardcodes FAR_PLANE = 60.0 and divides by it
// The projection must use the same far plane
var (_, proj) = ComputeFaceViewProj(Vector3.Zero, 0);
// M33 for perspective with M22 *= -1: should be negative
Assert.True(proj.M33 < 0, $"M33 should be negative for Vulkan projection, got {proj.M33}");
// M33 for perspective: should be negative (far/near-far)
Assert.True(proj.M33 < 0, $"M33 should be negative for perspective projection, got {proj.M33}");
}
static (Matrix4x4 view, Matrix4x4 proj) ComputeFaceViewProj(Vector3 lightPos, int face)
{
var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 2f, 1.0f, 0.1f, 60f);
proj.M22 *= -1;
var target = lightPos;
var up = Vector3.UnitY;
Vector3 up;
target += face switch
switch (face)
{
0 => Vector3.UnitX,
1 => -Vector3.UnitX,
2 => Vector3.UnitY,
3 => -Vector3.UnitY,
4 => Vector3.UnitZ,
5 => -Vector3.UnitZ,
_ => Vector3.UnitZ,
};
if (face == 2) up = -Vector3.UnitZ;
else if (face == 3) up = Vector3.UnitZ;
case 0: target += Vector3.UnitX; up = new Vector3(0, -1, 0); break;
case 1: target += -Vector3.UnitX; up = new Vector3(0, -1, 0); break;
case 2: target += Vector3.UnitY; up = new Vector3(0, 0, 1); break;
case 3: target += -Vector3.UnitY; up = new Vector3(0, 0, -1); break;
case 4: target += Vector3.UnitZ; up = new Vector3(0, -1, 0); break;
case 5: target += -Vector3.UnitZ; up = new Vector3(0, -1, 0); break;
default: target += Vector3.UnitZ; up = new Vector3(0, -1, 0); break;
}
var view = Matrix4x4.CreateLookAt(lightPos, target, up);
return (view, proj);