Draw a polygon QUADS when mouse is clicked? - opengl

Question

how can drawing like square or TRIANGLES when clicked on any position on screen show the shape this is my Attempt i do't know what doing
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#include <windows.h>
#include <gl/Gl.h>
#include <gl/glu.h>
#include <gl/glut.h>
GLsizei wh=500,ww=500;
GLfloat size=3.0;
void drawsquare( int x, int y)
{
y=wh-y;
glBegin(GL_POLYGON);
glVertex2f(x+size,y+size);
glVertex2f(x-size,y+size);
glVertex2f(x-size,y-size);
glVertex2f(x+size,y-size);
glEnd();
glFlush();
}
void mymose(int button,int state,int x,int y)
{
if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN)
drawsquare(x,y);
//if(button==GLUT_RIGHT_BUTTON_BUTTON && state==GLUT_UP)
// exit();
}
void myInit(){
glViewport(0,0,ww,wh);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);
glMatrixMode(GL_MODELVIEW);
glClearColor(0.0,0.0,0.0,1.0);
glColor3f(1.0,0.0,0.0);
}
int main(int argc, char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);
glutInitWindowSize(ww,wh);
glutInitWindowPosition(100,100);
glutCreateWindow("GLUT");
glutMouseFunc(mymose);
glutDisplayFunc(display);
glutMainLoop();
return 0;
}

Answer 1

You need a vector to store the points in.
Add points in the mouse callback and request a redraw via glutPostRedisplay().
Then in display() you can spin over all the points in the vector and draw quads around them:
#include <GL/glut.h>
#include <vector>
struct Point
{
Point( float x, float y ) : x(x), y(y) {}
float x, y;
};
std::vector< Point > points;
void mouse( int button, int state, int x, int y )
{
if( button == GLUT_LEFT_BUTTON && state == GLUT_UP )
{
points.push_back( Point( x, y ) );
}
if( button == GLUT_RIGHT_BUTTON && state == GLUT_UP )
{
points.clear();
}
glutPostRedisplay();
}
void display()
{
glClearColor( 0, 0, 0, 1 );
glClear( GL_COLOR_BUFFER_BIT );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
int w = glutGet( GLUT_WINDOW_WIDTH );
int h = glutGet( GLUT_WINDOW_HEIGHT );
glOrtho( 0, w, h, 0, -1, 1 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glColor3ub( 255, 0, 0 );
glBegin( GL_QUADS );
for( size_t i = 0; i < points.size(); ++i )
{
const unsigned int SIZE = 20;
const Point& pt = points[ i ];
glVertex2i( pt.x - SIZE, pt.y - SIZE );
glVertex2i( pt.x + SIZE, pt.y - SIZE );
glVertex2i( pt.x + SIZE, pt.y + SIZE );
glVertex2i( pt.x - SIZE, pt.y + SIZE );
}
glEnd();
glutSwapBuffers();
}
int main( int argc, char **argv )
{
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
glutInitWindowSize( 640, 480 );
glutCreateWindow( "GLUT" );
glutMouseFunc( mouse );
glutDisplayFunc( display );
glutMainLoop();
return 0;
}