build-matrix.h

// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: 2025-2026 Manuel Osorio
#pragma once
#include "flint/math/types.h"
 
#include <cmath>
 
namespace Flint {
  inline void buildModelMatrix(float out[16], const Vec2f &position, const Vec2f &size,
                               float rotation, const Vec2f &origin) {
    for (int i = 0; i < 16; ++i) {
      out[i] = (i % 5 == 0) ? 1.0f : 0.0f;
    }
 
    float cosA = std::cos(rotation);
    float sinA = std::sin(rotation);
 
    float tx = position.x - origin.x;
    float ty = position.y - origin.y;
 
    float sx = size.x;
    float sy = size.y;
 
    out[0] = cosA * sx;
    out[1] = sinA * sx;
    out[4] = -sinA * sy;
    out[5] = cosA * sy;
    if (rotation == 0.0f) {
      out[12] = tx;
      out[13] = ty;
    } else {
      out[12] = position.x + origin.x - (cosA * origin.x - sinA * origin.y);
      out[13] = position.y + origin.y - (sinA * origin.x + cosA * origin.y);
    }
  }
 
  inline void buildProjectionMatrix(float out[16], const FloatRect &cameraView) {
    for (int i = 0; i < 16; ++i) {
      out[i] = (i % 5 == 0) ? 1.0f : 0.0f;
    }
    out[0] = 2.0f / cameraView.size.x;
    out[5] = 2.0f / cameraView.size.y;
    out[12] = -(2.0f * cameraView.position.x + cameraView.size.x) / cameraView.size.x;
    out[13] = -(2.0f * cameraView.position.y + cameraView.size.y) / cameraView.size.y;
  }
}