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LibSoftGPU: Simplify Clipper interpolation

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By setting the clip plane normals' W coordinate to 1, we can skip two
coordinate retrievals and three additions. This works because the
Vector `.dot()` operation multiplies the W coordinates of both vectors.
This commit is contained in:
Jelle Raaijmakers 2022-04-17 20:51:11 +02:00 • committed by Andreas Kling
parent f680d82086
commit 838cee37a2
1 changed files with 11 additions and 11 deletions
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22
Userland/Libraries/LibSoftGPU/Clipper.cpp
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@ -1,6 +1,7 @@
/* /*
* Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com> * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
* Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org> * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
* Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
* Copyright (c) 2022, the SerenityOS developers. * Copyright (c) 2022, the SerenityOS developers.
* *
* SPDX-License-Identifier: BSD-2-Clause * SPDX-License-Identifier: BSD-2-Clause
@ -35,23 +36,22 @@ template<Clipper::ClipPlane plane>
static constexpr GPU::Vertex clip_intersection_point(GPU::Vertex const& p1, GPU::Vertex const& p2) static constexpr GPU::Vertex clip_intersection_point(GPU::Vertex const& p1, GPU::Vertex const& p2)
{ {
constexpr FloatVector4 clip_plane_normals[] = { constexpr FloatVector4 clip_plane_normals[] = {
{ 1, 0, 0, 0 }, // Left Plane { 1, 0, 0, 1 }, // Left Plane
{ -1, 0, 0, 0 }, // Right Plane { -1, 0, 0, 1 }, // Right Plane
{ 0, -1, 0, 0 }, // Top Plane { 0, -1, 0, 1 }, // Top Plane
{ 0, 1, 0, 0 }, // Bottom plane { 0, 1, 0, 1 }, // Bottom plane
{ 0, 0, 1, 0 }, // Near Plane { 0, 0, 1, 1 }, // Near Plane
{ 0, 0, -1, 0 } // Far Plane { 0, 0, -1, 1 } // Far Plane
}; };
constexpr auto clip_plane_normal = clip_plane_normals[to_underlying(plane)]; constexpr auto clip_plane_normal = clip_plane_normals[to_underlying(plane)];
// See https://www.microsoft.com/en-us/research/wp-content/uploads/1978/01/p245-blinn.pdf // See https://www.microsoft.com/en-us/research/wp-content/uploads/1978/01/p245-blinn.pdf
// "Clipping Using Homogeneous Coordinates" Blinn/Newell, 1978 // "Clipping Using Homogeneous Coordinates" Blinn/Newell, 1978
// Clip plane normals have W=1 so the vertices' W coordinates are included in x1 and x2.
float const w1 = p1.clip_coordinates.w(); auto const x1 = clip_plane_normal.dot(p1.clip_coordinates);
float const w2 = p2.clip_coordinates.w(); auto const x2 = clip_plane_normal.dot(p2.clip_coordinates);
float const x1 = clip_plane_normal.dot(p1.clip_coordinates); auto const a = x1 / (x1 - x2);
float const x2 = clip_plane_normal.dot(p2.clip_coordinates);
float const a = (w1 + x1) / ((w1 + x1) - (w2 + x2));
GPU::Vertex out; GPU::Vertex out;
out.position = mix(p1.position, p2.position, a); out.position = mix(p1.position, p2.position, a);