Gradient.h

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2025 Alex2772 and Contributors
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#pragma once
 
#include "AUI/Image/AImage.h"
#include "AUI/Render/ABrush.h"
 
namespace aui::render::brush::gradient {
   struct Helper {
   public:
       ASmallVector<glm::u8vec4, 8> colors;
       glm::mat3 matrix;
 
       Helper(const ALinearGradientBrush& brush) {
           for (const auto& c : brush.colors) {
               colors.push_back(glm::uvec4(c.color * 255.f));
           }
           //float actualEdgeUvPosition = (0.5f - 0.05f /* bias to make ideal color edge */) / float(colors.size());
           float actualEdgeUvPosition = 0.f; // temporary
 
           float rotationRadians = brush.rotation.radians();
 
           float s = glm::sin(rotationRadians);
           float c = -glm::cos(rotationRadians);
           float bias = glm::max(-s, -c, 0.f);
 
           auto probe = [&](glm::vec2 uv) {
               return uv.x * s + uv.y * c + bias;
           };
           auto adjust = [&](glm::vec2 uv) {
               float p = probe(uv);
               if (p > 1.f) {
                   s /= p;
                   c /= p;
                   bias /= p;
               }
           };
 
           if (auto p = probe({1, 1}); p < 0.f) {
               bias += -p;
           }
 
           adjust({0, 0});
           adjust({1, 0});
           adjust({0, 1});
           adjust({1, 1});
 
           matrix = {
               /* uv.x */ s * (1.f - actualEdgeUvPosition * 2.f), 0.f, 0.f,
               /* uv.y */ c * (1.f - actualEdgeUvPosition * 2.f), 0.f, 0.f,
               /* 1    */ bias * (1.f - actualEdgeUvPosition * 2.f) + actualEdgeUvPosition, 0.f, 0.f,
           };
       }
 
       [[nodiscard]]
       AImageView gradientMap() const noexcept {
           return AImageView({(const char*)colors.data(), colors.sizeInBytes()}, {colors.size(), 1}, APixelFormat::RGBA_BYTE);
       }
   };
}

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