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gl_rasterizer: Fix issue with interpolation of opposite quaternions.

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This commit is contained in:
bunnei 2016-01-28 23:29:33 -05:00
parent b694423d09
commit 8e9318f20a
2 changed files with 32 additions and 4 deletions
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28
src/video_core/renderer_opengl/gl_rasterizer.cpp
View file

@ -158,12 +158,34 @@ void RasterizerOpenGL::Reset() {
res_cache.InvalidateAll();
}
/**
* This is a helper function to resolve an issue with opposite quaternions being interpolated by
* OpenGL. See below for a detailed description of this issue (yuriks):
*
* For any rotation, there are two quaternions Q, and -Q, that represent the same rotation. If you
* interpolate two quaternions that are opposite, instead of going from one rotation to another
* using the shortest path, you'll go around the longest path. You can test if two quaternions are
* opposite by checking if Dot(Q1, W2) < 0. In that case, you can flip either of them, therefore
* making Dot(-Q1, W2) positive.
*
* NOTE: This solution corrects this issue per-vertex before passing the quaternions to OpenGL. This
* should be correct for nearly all cases, however a more correct implementation (but less trivial
* and perhaps unnecessary) would be to handle this per-fragment, by interpolating the quaternions
* manually using two Lerps, and doing this correction before each Lerp.
*/
static bool AreQuaternionsOpposite(Math::Vec4<Pica::float24> qa, Math::Vec4<Pica::float24> qb) {
Math::Vec4f a{ qa.x.ToFloat32(), qa.y.ToFloat32(), qa.z.ToFloat32(), qa.w.ToFloat32() };
Math::Vec4f b{ qb.x.ToFloat32(), qb.y.ToFloat32(), qb.z.ToFloat32(), qb.w.ToFloat32() };
return (Math::Dot(a, b) < 0.f);
}
void RasterizerOpenGL::AddTriangle(const Pica::Shader::OutputVertex& v0,
const Pica::Shader::OutputVertex& v1,
const Pica::Shader::OutputVertex& v2) {
vertex_batch.emplace_back(v0);
vertex_batch.emplace_back(v1);
vertex_batch.emplace_back(v2);
vertex_batch.emplace_back(v0, false);
vertex_batch.emplace_back(v1, AreQuaternionsOpposite(v0.quat, v1.quat));
vertex_batch.emplace_back(v2, AreQuaternionsOpposite(v0.quat, v2.quat));
}
void RasterizerOpenGL::DrawTriangles() {

8
src/video_core/renderer_opengl/gl_rasterizer.h
View file

@ -248,7 +248,7 @@ private:
/// Structure that the hardware rendered vertices are composed of
struct HardwareVertex {
HardwareVertex(const Pica::Shader::OutputVertex& v) {
HardwareVertex(const Pica::Shader::OutputVertex& v, bool flip_quaternion) {
position[0] = v.pos.x.ToFloat32();
position[1] = v.pos.y.ToFloat32();
position[2] = v.pos.z.ToFloat32();
@ -270,6 +270,12 @@ private:
view[0] = v.view.x.ToFloat32();
view[1] = v.view.y.ToFloat32();
view[2] = v.view.z.ToFloat32();
if (flip_quaternion) {
for (float& x : normquat) {
x = -x;
}
}
}
GLfloat position[4];