CODEWITHSUNDEEP
opengl
user5329895
user5329895

Reputation:

How to draw consecutive points on mouse drag with OpenGL

I am making a basic OpenGL program which like PAINT program on windows.

Description: If I drag the mouse on the window screen then after I release the button(left) a consecutive points should appear that shows the path of dragging the mouse.

My code just works with a point on screen. I want to draw points such as line but I have no idea what I do.

Here is my code:

#include <windows.h>
#include <math.h>
#include <gl/glut.h>
#include <gl/gl.h>
void myDisplay(void) {
    glClear(GL_COLOR_BUFFER_BIT);
    glFlush();
}
void myMouse(int button, int state, int x, int y)
{
    int yy;
    yy = glutGet(GLUT_WINDOW_HEIGHT);
    y = yy - y; /* In Glut, Y coordinate increases from top to bottom */
    glColor3f(1.0, 0, 0);
    if ((button == GLUT_LEFT_BUTTON) && (state == GLUT_DOWN))
    {
        glBegin(GL_POINTS);
        glVertex2i(x, y);
        glEnd();
    }
    glFlush();
}
void myInit(void)
{
    glClearColor(1.0f, 1.0f, 1.0f, 0.0);
    glColor3f(1.0f, 1.0f, 1.0f);
    glPointSize(5.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0, 640.0, 0.0, 480.0);
}
void main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(640, 480);
    glutInitWindowPosition(100, 150);
    glutCreateWindow("Draw Pixel");
    glutDisplayFunc(myDisplay);
    glutMouseFunc(myMouse);
/*glutMotionFunc(myPressedMove);*/
    myInit();
    glutMainLoop();
}

Upvotes: 0

Views: 1981

Answers (1)

genpfault
genpfault

Reputation: 52082

Append mouse coordinates to an array in glutMouseFunc(), issue a glutPostRedisplay(), and draw array in glutDisplayFunc():

#include <gl/glut.h>
#include <vector>

std::vector< float > points;
void myMouse(int button, int state, int x, int y)
{
    int yy;
    yy = glutGet(GLUT_WINDOW_HEIGHT);
    y = yy - y; /* In Glut, Y coordinate increases from top to bottom */
    if( (button == GLUT_LEFT_BUTTON) && (state == GLUT_DOWN) )
    {
        points.push_back(x);
        points.push_back(y);
    }

    glutPostRedisplay();
}

void myDisplay(void)
{
    glClearColor(1.0f, 1.0f, 1.0f, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0, 640.0, 0.0, 480.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glPointSize(5.0);
    glBegin(GL_POINTS);
    glColor3f(1.0f, 1.0f, 1.0f);
    for (size_t i = 0; i < points.size(); i += 2)
    {
        glVertex2i( points[i], points[i+1] );
    }
    glEnd();

    glFlush();
}

void main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(640, 480);
    glutInitWindowPosition(100, 150);
    glutCreateWindow("Draw Pixel");
    glutDisplayFunc(myDisplay);
    glutMouseFunc(myMouse);
    glutMainLoop();
}

Upvotes: 1

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