src/gl/partrenderer.cpp

#include <QMouseEvent>
#include <GL/glut.h> // teapot
#include "partrenderer.h"

PartRenderer::PartRenderer(QWidget* parent) :
	QOpenGLWidget{parent}
{
	this->setMouseTracking(true);
}

void PartRenderer::initializeGL()
{
	this->initializeOpenGLFunctions();
	if (this->glGetError() != GL_NO_ERROR)
	{
		abort();
	}
	this->initializeLighting();
	this->initialized = true;
	this->rotation = QQuaternion::fromAxisAndAngle({1, 0, 0}, 30);
	this->rotation *= QQuaternion::fromAxisAndAngle({0, 1, 0}, 330);
}

// https://stackoverflow.com/a/12943456
static void perspectiveGL(GLdouble fovY, GLdouble aspect, GLdouble zNear, GLdouble zFar)
{
	//fH = tan( (fovY / 2) / 180 * pi ) * zNear;
	const GLdouble fH = std::tan(fovY / 360 * pi) * zNear;
	const GLdouble fW = fH * aspect;
	glFrustum(-fW, fW, -fH, fH, zNear, zFar);
}

/*
 * Pads a 3×3 matrix into a 4×4 one by adding cells from the identity matrix.
 */
static QMatrix4x4 padMatrix(const QMatrix3x3& stub)
{
	return {
		stub(0, 0), stub(0, 1), stub(0, 2), 0,
		stub(1, 0), stub(1, 1), stub(1, 2), 0,
		stub(2, 0), stub(2, 1), stub(2, 2), 0,
		0, 0, 0, 1
	};
}


void PartRenderer::initializeLighting()
{
	GLfloat materialShininess[] = {5.0};
	GLfloat lightPosition[] = {1.0, 1.0, 1.0, 0.0};
	GLfloat ambientLightingLevel[] = {0.5, 0.5, 0.5, 1.0};
	glShadeModel(GL_SMOOTH);
	glMaterialfv(GL_FRONT, GL_SHININESS, materialShininess);
	glLightfv(GL_LIGHT0, GL_AMBIENT, ambientLightingLevel);
	glLightfv(GL_LIGHT0, GL_DIFFUSE, ambientLightingLevel);
	glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);
	glEnable(GL_COLOR_MATERIAL);
	glEnable(GL_DEPTH_TEST);
}

void PartRenderer::resizeGL(int width, int height)
{
	constexpr GLfloat near = 1.0f;
	constexpr GLfloat far = 1.0e+05f;
	glViewport (0, 0, width, height);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	::perspectiveGL(45.0f, static_cast<double>(width) / static_cast<double>(height), near, far);
	glMatrixMode(GL_MODELVIEW);
}

// https://www.codemiles.com/c-opengl-examples/drawing-teapot-using-opengl-t9010.html?mobile=on
void PartRenderer::paintGL()
{
	glMatrixMode(GL_MODELVIEW);
	// clear the drawing buffer.
	glClear(GL_COLOR_BUFFER_BIT);
	// clear the identity matrix.
	glLoadIdentity();
	// traslate the draw by z = -4.0
	// Note this when you decrease z like -8.0 the drawing will looks far , or smaller.
	glTranslatef(0.0,0.0,-4.5);
	// Red color used to draw.
	glColor3f(0.8, 0.2, 0.1);
	glMultMatrixf(padMatrix(this->rotation.toRotationMatrix()).constData());
	glutSolidTeapot(1.0);
	glFlush();
}

static QPointF pointToPointF(const QPoint& point)
{
	return {static_cast<qreal>(point.x()), static_cast<qreal>(point.y())};
}

/*
static QPoint pointFToPoint(const QPointF& point)
{
	return {static_cast<int>(std::round(point.x())), static_cast<int>(std::round(point.y()))};
}
*/

void PartRenderer::mouseMoveEvent(QMouseEvent* event)
{
	const bool left = event->buttons() & Qt::LeftButton;
	const QPointF move = pointToPointF(event->pos()) - this->lastMousePosition;
	if (left and not move.isNull())
	{
		const QQuaternion versor = QQuaternion::fromAxisAndAngle(
			QVector3D{static_cast<float>(move.y()), static_cast<float>(move.x()), 0.0f},
			0.6 * std::hypot(move.x(), move.y())
		);
		this->rotation = versor * this->rotation;
		this->update();
	}
	this->lastMousePosition = pointToPointF(event->pos());
}