mirror of
https://github.com/MobileGL-Dev/MobileGL
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42 lines
2.1 KiB
C++
42 lines
2.1 KiB
C++
// MobileGL - MobileGL/MG_Util/ShaderTranspiler/SpirvPasses/EmulateNoPerspectivePass.h
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// Copyright (c) 2025-2026 MobileGL-Dev
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// Licensed under the GNU Lesser General Public License v3.0:
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// https://www.gnu.org/licenses/gpl-3.0.txt
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// https://www.gnu.org/licenses/lgpl-3.0.txt
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// SPDX-License-Identifier: LGPL-3.0-only
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// End of Source File Header
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#pragma once
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#include "source/opt/pass.h"
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#include "spirv-tools/optimizer.hpp"
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#include <Includes.h>
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namespace MobileGL {
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namespace MG_Util {
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namespace ShaderTranspiler {
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// Emulates 'noperspective' (screen-linear) interpolation on GLES devices that lack
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// GL_NV_shader_noperspective_interpolation, so no NV extension is required. The hardware
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// interpolates perspective-correct; screen-linear L(a) is recovered from the identity
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// L(a) = P(a * w) * gl_FragCoord.w
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// where P is perspective-correct interpolation and w is the vertex clip-space w. So each
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// NoPerspective-decorated output is pre-multiplied by gl_Position.w in the vertex stage
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// and each NoPerspective-decorated input is multiplied by gl_FragCoord.w in the fragment
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// stage; the decoration is then removed so the varying transports smooth. This is exact
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// (modulo float precision - the emulated varyings want highp).
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//
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// Scope: plain interface variables of float or floatN type. Anything it cannot emulate
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// (interface-block members, matrices, or a stage lacking the needed builtin) has its
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// NoPerspective decoration stripped instead, degrading to smooth - the same result the
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// extension-less fallback produced before, and never invalid SPIR-V. DirectGLES only.
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class EmulateNoPerspectivePass : public spvtools::opt::Pass {
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public:
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const char* name() const override { return "emulate-noperspective"; }
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Status Process() override;
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static spvtools::Optimizer::PassToken CreateEmulateNoPerspectivePass();
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};
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} // namespace ShaderTranspiler
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} // namespace MG_Util
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} // namespace MobileGL
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