Line won't appear in opengl - c++

I am trying to draw a simple line in opengl and i have set up the environemt properly and when executing the code i get a blank screen rather than the line.
This is my code
#include "stdafx.h"
#include "freeglut.h"
#include <Windows.h>
#include <iostream>
using namespace std;
void reshape(int w, int h)
{
glViewport(0, 0, w, h);
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glutSwapBuffers();
glColor3f(1.0, 0.0, 0.0);
glPointSize(5.0);
glLineWidth(5.0);
glBegin(GL_LINES);
glVertex2d(0.0, 0.0);
glVertex2d(0.5,0.5);
glEnd();
}
int main(int argc, char* argv[]) {
// Initialize GLUT
glutInit(&argc, argv);
// Set up some memory buffers for our display
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
// Set the window size
glutInitWindowSize(800, 600);
// Create the window with the title "Hello,GL"
glutCreateWindow("Hello, GL");
// Bind the two functions (above) to respond when necessary
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutMainLoop();
return 0;
}

In your display function you have swapped the buffers before the line is drawn. you have to swap the buffers after the line is drawn . so your code should appear as follows:
void display()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(1.0, 0.0, 0.0);
glPointSize(5.0);
glLineWidth(5.0);
glBegin(GL_LINES);
glVertex2d(0.0, 0.0);
glVertex2d(0.5,0.5);
glEnd();
glutSwapBuffers();
}

Related

Visual Studio Express 2017 Output not displaying for stroke text function

I've been trying to run this program in visual studio express 2017. Using opengl.
I found the rendering code and stroke code in a pdf and was trying it out but first it showed many errors, once taken care of I compiled the program. Although the run was without any errors the output screen remains blank.
#include "stdafx.h"
#include <windows.h>
#include <gl/GL.h>
#include <glut.h>
#include <gl/GLU.h>
void myInit(void)
{
glClearColor(1.0, 1.0, 1.0, 0.0);
glColor3f(0.0f, 0.0f, 0.0f);
glMatrixMode(GL_PROJECTION);
glLineWidth(6.0);
glLoadIdentity();
gluOrtho2D(0.0, 700, 0.0, 700);
}
void drawStrokeText(const char *string, int x, int y, int z)
{
const char *c;
glPushMatrix();
glTranslatef(x, y + 8, z);
glScalef(0.09f, -0.08f, z);
for (c = string; *c != '\0'; c++)
{
glutStrokeCharacter(GLUT_STROKE_ROMAN, *c);
}
glPopMatrix();
}
void render()
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glColor3ub(255, 50, 255);
drawStrokeText("Hello", 300, 400, 0);
glutSwapBuffers();
}
void myDisplay(void)
{
glClear(GL_COLOR_BUFFER_BIT);
render();
glFlush();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(700, 700);
glutInitWindowPosition(100, 150);
glutCreateWindow("My First Program");
glutDisplayFunc(myDisplay);
myInit();
glutMainLoop();
}
Matrix mode is switched to GL_PROJECTION in myInit but never switched back. Therefore the glLoadIdentity() instruction in render will override the projection matrix. You have to switch the matrix mode to GL_MODELVIEW before glLoadIdentity():
void render()
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW); // <--
glLoadIdentity();
glColor3ub(255, 50, 255);
drawStrokeText("Hello", 300, 400, 0);
glutSwapBuffers();
}

How can i draw two object in the same window in openGL c++?

I'm trying to draw 2 different objects in Visual Studio using OpenGL.
I can't seem to draw both object at the same time in the same window. I Tried putting both object in the same function, but it only display one object in the window.
#include<Windows.h>
#include<glut.h>
#include<stdlib.h>
#include<iostream>
using namespace std;
void init()
{
glClearColor(0, 0.4, 1, 0.0);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(0.0, 800, 0.0, 600);
}
void kapal()
{
//badan
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POLYGON);
glColor3ub(148, 111, 70);
glVertex2i(20 , 100);
glVertex2i(160 , 100);
glColor3ub(107, 65, 17);
glVertex2i(140 , 60 );
glVertex2i(40 , 60);
glColor3ub(9, 5, 0);
glEnd();
//tiang
glColor3ub(97, 65, 28);
glLineWidth(5);
glBegin(GL_LINES);
glVertex2i(90 ,100 );
glVertex2i(90 , 160 );
glEnd();
//layar
glColor3ub(215, 215, 215);
glBegin(GL_TRIANGLES);
glVertex2i(90, 160 );
glVertex2i(120 , 130 );
glVertex2i(90 , 130);
glEnd();
glFlush();
}
void mobil()
{
//bawah
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POLYGON);
glColor3ub(148, 111, 70);
glVertex2i(100, 170);
glVertex2i(100, 230);
glVertex2i(450, 230);
glVertex2i(450, 170);
glEnd();
//atas
glBegin(GL_POLYGON);
glColor3ub(148, 111, 70);
glVertex2i(150, 230);
glVertex2i(200, 270);
glVertex2i(400, 270);
glVertex2i(450, 230);
glEnd();
glFlush();
}
static void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
kapal();
mobil();
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowPosition(100, 100);
glutInitWindowSize(800, 600);
glutCreateWindow("Kapal APi ");
init();
glutDisplayFunc(display);
glutMainLoop();
}
As you can see void kapal() is the first object and void mobil() is the second.
This the result that i got:
Is there anyway to fix this so i can display both objects in the same windows?
The issue is that you call glClear(GL_COLOR_BUFFER_BIT); before drawing an object.
Clear the framebuffer before drawing anything, but not before drawing a specific object.
static void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // <-- this is OK
kapal();
mobil();
glutSwapBuffers();
}
void kapal()
{
//badan
// glClear(GL_COLOR_BUFFER_BIT); <--- DELETE
// [...]
}
void mobil()
{
//bawah
// glClear(GL_COLOR_BUFFER_BIT); <--- DELETE
// [...]
}

OpenGL with GLUT. Not Drawing?

#include <GL/gl.h>
#include <GL/glut.h>
void display();
void init();
int main(int argc, char* argv[])
{
init();
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowSize(320, 240);
glutCreateWindow("Main Window");
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
void init()
{
glDisable(GL_DEPTH_TEST);
}
void display()
{
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glBegin(GL_QUADS);
glColor3i(255,255,255);
glVertex2f(10, 10);
glVertex2f(100, 10);
glVertex2f(100, 100);
glVertex2f(10, 100);
glEnd();
glutSwapBuffers();
}
Theoretically, this code should draw a white rectangle. But all I see is a black empty screen. What's wrong?
Here is my working example with the changes I made noted by comments:
#include <gl/glut.h>
#include <gl/gl.h>
#define WINDOW_WIDTH 320
#define WINDOW_HEIGHT 240
void display();
void init();
int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowSize(WINDOW_WIDTH, WINDOW_HEIGHT);
glutCreateWindow("Main Window");
init(); // changed the init function to come directly before display function
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
void init()
{
glClearColor(0, 0, 0, 0); // moved this line to be in the init function
glDisable(GL_DEPTH_TEST);
// next four lines are new
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, WINDOW_WIDTH-1, WINDOW_HEIGHT-1, 0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glBegin(GL_QUADS);
glColor3ub(255,255,255); // changed glColor3i to glColor3ub (see below)
glVertex2f(10, 10);
glVertex2f(100, 10);
glVertex2f(100, 100);
glVertex2f(10, 100);
glEnd();
glFlush(); // added this line
//glutSwapBuffers(); // removed this line
}
glColor3ub is the function you want to use if you want to provide colors in the 0-255 range.
Hope this helps.

OpenGL Line Drawing

I am practicing the exercises from my textbook but I could not get the outputs that I should.
Here is what I have :
#include <math.h>
#include <GLUT/glut.h>
#include <OpenGL/OpenGL.h>
//Initialize OpenGL
void init(void) {
glClearColor(0.0,0.0,0.0,0.0);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(0.0,300.0,0.0,300.0);
}
void drawLines(void) {
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0,0.4,0.2);
glPointSize(3.0);
glBegin(GL_LINES);
glVertex2d(180, 15);
glVertex2d(10, 145);
glEnd();
}
int main(int argc, char**argv) {
glutInit(&argc, argv);
glutInitWindowPosition(10,10);
glutInitWindowSize(500,500);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutCreateWindow("Example");
init();
glutDisplayFunc(drawLines);
glutMainLoop();
}
When I run this piece of code, I get completely blank white screen.
i'm also not an expert on OpenGL but the problem is that you haven't set a viewport to where your scene should be projected. Your init should look somewhat like this:
glClearColor(0, 0, 0, 0);
glViewport(0, 0, 500, 500);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 500, 0, 500, 1, -1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
You also need to put a glFlush(); after your drawing.
void drawLines(void) {
...
glFlush();
}
Determine and draw the output of OpenGL sub function below:
1.
glColor3f(0.0, 0.0, 0.0, 0.0);
glBegin(Gl_LINES);
glVertex2i (200, 200);
glVertex2i (70, 20);
glVertex2i (120, 150);
glVertex2i (200, 20);
glVertex2i (60, 100);
glEnd();
int p1[]={200,100};
int p2[]={70,20};
int p3[]={120,150};
int p4[]={200,20};
int p5[]={60,100};
glBegin(GL_LINE_STRIP);
glVertex2iv (p1);
glVertex2iv (p2);
glVertex2iv (p3);
glVertex2iv (p4);
glVertex2iv (p5);
glEnd();

Point doesn't show in OpenGL

I am trying to draw a point using OpenGL like below, but it only displays a black window. Can someone tell me what's the error?
#include "stdafx.h"
#include <gl/GL.h>
#include <gl/GLU.h>
#include <gl/glut.h>
void init(void)
{
glClearColor(0.0,0.0,0.0,0.0);
glColor3f(1.0,0,1.0);
glPointSize(10);
//glShadeModel(GL_FLAT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D (0.0,0.0,400, 150);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
float pointSize = 5;
glPointSize(10);
glBegin(GL_POINTS); // render with points
glVertex2i(50,40); //display a point
glEnd();
glFlush();
}
void reshape(int w,int h)
{
glViewport(0,0,(GLsizei)w,(GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0,(GLdouble)w,0.0,(GLdouble)h,-1.0,1.0);
}
int _tmain(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
glutInitWindowPosition(100, 100);
glutInitWindowSize(400, 150);
glutCreateWindow("Draw Simple Object");
init();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
The parameters you're passing to gluOrtho2d look wrong. The order is left, right, top, bottom. You've set both the left and right to 0.0. Based on your glutInitWindowSize call, I'd guess what you want is something like gluOrtho2d(0.0, 400.0, 0.0, 150.0); (or maybe gluOrtho2d(0.0, 400.0, 150.0, 0.0);) instead.
Could it be that the points you draw are black and the background is, too?
Have you tried adding this line to the beginning of your display function:
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);