siimageviewer.h

/*
Licensed under the MIT License <http://opensource.org/licenses/MIT>.
SPDX-License-Identifier: MIT
Copyright (c) 2023 Stefan Isak <http://sisak.at>.

Permission is hereby  granted, free of charge, to any  person obtaining a copy
of this software and associated  documentation files (the "Software"), to deal
in the Software  without restriction, including without  limitation the rights
to  use, copy,  modify, merge,  publish, distribute,  sublicense, and/or  sell
copies  of  the Software,  and  to  permit persons  to  whom  the Software  is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE  IS PROVIDED "AS  IS", WITHOUT WARRANTY  OF ANY KIND,  EXPRESS OR
IMPLIED,  INCLUDING BUT  NOT  LIMITED TO  THE  WARRANTIES OF  MERCHANTABILITY,
FITNESS FOR  A PARTICULAR PURPOSE AND  NONINFRINGEMENT. IN NO EVENT  SHALL THE
AUTHORS  OR COPYRIGHT  HOLDERS  BE  LIABLE FOR  ANY  CLAIM,  DAMAGES OR  OTHER
LIABILITY, WHETHER IN AN ACTION OF  CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#ifndef SIIMAGEVIEWER_H
#define SIIMAGEVIEWER_H

#include <QOpenGLFunctions>
#include <QOpenGLFunctions_3_3_Core>
#include <QOpenGLWidget>
#include <QMatrix4x4>
#include <QVector2D>
#include <QVector4D>

class SiImageViewer : public QOpenGLWidget, protected QOpenGLFunctions_3_3_Core
{
    Q_OBJECT
public:
    explicit SiImageViewer(QWidget *parent = nullptr);
    ~SiImageViewer();

    /**
     * @brief Sets the main image. The data is directly copied onto graphics memory.
     * The provided QImage can be destroyed after the call.
     * @param image Image to display.
     */
    void setImage(const QImage& image);

    /**
     * @brief Sets the background color of the viewer.
     * @param color Background color
     */
    void setBackground(const QColor& color);

    /**
     * @brief Resets all user actions (rotations, translations, zoom).
     */
    void reset();

    /**
     * @brief Rotates the image counter-clockwise around the image center.
     * @param angleDeg Angle in degrees.
     */
    void rotate(float angleDeg);

    /**
     * @brief Rotates the image counter-clockwise around the given point.
     * @param angleDeg Angle in degrees.
     * @param point Rotation center
     */
    void rotateAround(float angleDeg, const QPoint& point);

    /**
     * @brief Translates the image x, y amount of pixels.
     * @param x Amount in x direction.
     * @param y Amount in y direction.
     */
    void translate(float x, float y);

protected:
    void initializeGL() override;
    void paintGL() override;
    void resizeGL(int width, int height) override;
    void mousePressEvent(QMouseEvent *event) override;
    void mouseReleaseEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;
    void wheelEvent(QWheelEvent *event) override;
    void keyPressEvent(QKeyEvent *event) override;
    void keyReleaseEvent(QKeyEvent *event) override;
    void focusInEvent(QFocusEvent *event) override;

private:
    GLuint m_vertexShader;
    GLuint m_fragmentShader;
    GLuint m_shaderProgram;
    GLuint m_vao;
    GLuint m_vbo;
    GLuint m_ibo;
    GLuint m_texture;

    // Unifrom locations
    GLuint m_textureLocation;
    GLuint m_mvpLocation;

    int32_t m_imageWidth{1};
    int32_t m_imageHeight{1};
    QColor m_backgroundColor;

    QMatrix4x4 m_pre;        // used to transform the vertex coordinates to match the image dimension
    QMatrix4x4 m_model;      // used for global transformations (user rotation, scaling, ...)
    QMatrix4x4 m_view;       // used for viewport transformation
    QMatrix4x4 m_projection; // not in use
    QMatrix4x4 m_mvp;        // multiplication of projection, view, model, pre
    QVector2D m_cursorPosImage;   // cursor position in image coordinates
    QVector2D m_originalMousePos; // cursor position on first mouse down
    QVector2D m_mouseDownPos;     // cursor position from mouse down event

    float m_scale{1.0}; // current scaling amount to apply
    float m_zoomStep;   // scaling factor for one scroll wheel change

    bool m_panning;   // true when middle mouse button is held down
    bool m_shiftDown; // true when shift is held down
    bool m_ctrlDown;  // true when control is held down
    bool m_rDown;     // true when R is held down

    void resetStates();
    void setupShaders();
    void setupBuffers();
    void setupTexture();
    void setupMatrices();
    void updateMatrices();
    void centerImage();

    /**
     * @brief Gets the current cursor position relative to the widget.
     * @return Relative cursor position
     */
    QVector2D currentCursorPos() const;

    /**
     * @brief Unprojects an screen point back to the image.
     * @param screen A point in screen coordinates.
     * @return Image coordinates in pixels.
     */
    QVector2D screenToImage(const QVector2D& screen);

    /**
     * @brief Projects an image point onto the screen.
     * @param image A point in image coordinates (pixels).
     * @return Screen coordinates in pixels.
     */
    QVector2D imageToScreen(const QVector2D& image);
};

#endif // SIIMAGEVIEWER_H