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binarydude87
06-22-2014, 05:56 AM
This is my first time using opengl and I am experimenting with adding/drawing polygons/points/etc. on top of a PPM image. The image is already loaded when the application runs. My attempt to draw a square is from lines 30 - 35. The program runs but the square is not present. Just the image. Any help is appreciated.



#include<windows.h>
#include <stdio.h>
#include <stdlib.h>
#include<Gl/gl.h>
#include<GL/glut.h>

int n;
int m;

int *image;

void myInit (void)
{
glClearColor ( 1.0, 1.0, 1.0 , 1.0);
glColor3f ( 1.0f, 0.0f, 0.0f );
glPointSize ( 4.0 );
glMatrixMode ( GL_PROJECTION );
glLoadIdentity ( );
gluOrtho2D ( 0.0, 400.0, 1.0, 400.0 );
}


void display(void)
{

glClear ( GL_COLOR_BUFFER_BIT );
glRasterPos2i(0,0);
glDrawPixels(n,m,GL_RGB, GL_UNSIGNED_INT, image);
glPointSize(10.0);
glBegin(GL_POLYGON);
glVertex2f(-0.5, -0.5);
glVertex2f(-0.5, 0.5);
glVertex2f(0.5, 0.5);
glVertex2f(0.5, -0.5);
glEnd();
glFlush ( );

}

void myreshape(int h, int w)
{
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLfloat) n, 0.0, (GLfloat) m);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glViewport(0,0,h,w);
}

int main(int argc, char**argv)
{
FILE *fd;
int k, nm;
char c;
char b[70];
float s;
char red, green, blue;
int x, y;

fd = fopen("map.ppm", "r");
if(fd == 0)
{
exit(0);
}


fscanf(fd, "%s", b);
if((b[0] != 'P') || (b[1] != '6'))
{
printf("%s is not a PPM file!\n", b);
exit(0);
}

fscanf(fd, "%c", &c);

fscanf(fd, "%c", &c);
while(c == '#')
{
fscanf(fd, "%[^\n]", b);
printf("%s\n", b);
fscanf(fd, "%c", &c);
printf("%c", c);
}

ungetc(c,fd);

fscanf(fd, "%d %d %d", &n, &m, &k);

printf("%d rows %d colums max value = %d\n", n, m, k);

nm = n*m;

image = (int*)malloc(3*sizeof(GLint)*nm);

s = 255./k;

for(x = 0; x < m; x++)
{
for(y = n-1; y >= 0; y--)
{
fscanf(fd, "%c", &red);
fscanf(fd, "%c", &green);
fscanf(fd, "%c", &blue);

image[3*nm - 3*(x*n +y) -3] = green;
image[3*nm - 3*(x*n +y) -2] = blue;
image[3*nm - 3*(x*n +y) -1] = red;

}
}


glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(n,m);
glutInitWindowPosition(0,0);
glutCreateWindow("Little BigHorn");
glutReshapeFunc(myreshape);
glutDisplayFunc(display);
glPixelTransferf(GL_RED_SCALE, s);
glPixelTransferf(GL_GREEN_SCALE, s);
glPixelTransferf(GL_BLUE_SCALE, s);
glPixelStorei(GL_UNPACK_SWAP_BYTES, GL_TRUE);
glClearColor(1.0, 1.0, 1.0, 1.0);
myInit ( );
glutMainLoop ( );
}

carsten neumann
06-22-2014, 06:27 AM
Your chosen projection and the coordinates of your polygon's vertices don't fit together.



gluOrtho2D ( 0.0, 400.0, 1.0, 400.0 );


This makes vertices with x in [0,400] and y in [1,400] project to your screen, but your vertex positions are in [-0.5,0.5].

binarydude87
06-22-2014, 12:51 PM
Wooooooowwwww....I feel stupid. Thank you very much!