Moving a lot of Shapes in Opengl - c++

Question

In this post the rectangle moved via mouse. I want to add a triangle and move like rectangle via mouse.
The triangle function like this:
void drawTriangle(float x,float y,float size){
glPushMatrix();
glTranslatef( x, y, 0.0f );
glScalef( size, size, 1.0f );
glBegin( GL_TRIANGLES );
glColor3ub( 255, 255, 255 );
glVertex2f( -1, 1 );
glVertex2f( 1, -1 );
glVertex2f( 1, 1 );
glEnd();
glPopMatrix();
Rectangle and triangle moved together. But I want to move it different. So what is my wrong?

Answer 1

You'll have to maintain an array of Shape objects and test each one for mouse collisions, as well as keep track of which Shape you're dragging:
#include <GL/glut.h>
#include <vector>
using namespace std;
struct Shape
{
float mX, mY;
float mSize;
bool mIsRectangle;
bool PointInside( const float x, const float y ) const
{
return
mX - mSize <= x && x <= mX + mSize
&&
mY - mSize <= y && y <= mY + mSize;
}
};
vector< Shape > objects;
Shape* dragging = NULL;
void mouse( int button, int state, int x, int y )
{
if( GLUT_DOWN == state )
{
dragging = NULL;
for( Shape& obj : objects )
{
if( obj.PointInside( x, y ) )
{
dragging = &obj;
glutPostRedisplay();
break;
}
}
}
else
{
dragging = NULL;
}
}
void motion( int x, int y )
{
if( dragging )
{
dragging->mX = x;
dragging->mY = y;
glutPostRedisplay();
}
}
void drawRect( float x, float y, float size )
{
glPushMatrix();
glTranslatef( x, y, 0.0f );
glScalef( size, size, 1.0f );
glBegin( GL_QUADS );
glColor3ub( 255, 255, 255 );
glVertex2f( -1, -1 );
glVertex2f( 1, -1 );
glVertex2f( 1, 1 );
glVertex2f( -1, 1 );
glEnd();
glPopMatrix();
}
void drawTriangle( float x, float y, float size )
{
glPushMatrix();
glTranslatef( x, y, 0.0f );
glScalef( size, size, 1.0f );
glBegin( GL_TRIANGLES );
glColor3ub( 255, 255, 255 );
glVertex2f( -1, 1 );
glVertex2f( 1, -1 );
glVertex2f( 1, 1 );
glEnd();
glPopMatrix();
}
void display()
{
glClearColor( 0, 0, 0, 1 );
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
const double w = glutGet( GLUT_WINDOW_WIDTH );
const double h = glutGet( GLUT_WINDOW_HEIGHT );
glOrtho( 0, w, h, 0, -1, 1 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
for( const Shape& obj : objects )
{
if( obj.mIsRectangle )
drawRect( obj.mX, obj.mY, obj.mSize );
else
drawTriangle( obj.mX, obj.mY, obj.mSize );
}
glutSwapBuffers();
}
int main(int argc, char **argv)
{
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE );
glutInitWindowSize( 600, 600 );
glutCreateWindow( "GLUT" );
glutDisplayFunc( display );
glutMouseFunc( mouse );
glutMotionFunc( motion );
Shape temp;
temp.mSize = 50;
temp.mX = temp.mY = 100;
temp.mIsRectangle = true;
objects.push_back( temp );
temp.mX = temp.mY = 200;
temp.mIsRectangle = false;
objects.push_back( temp );
glutMainLoop();
return 0;
}