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chuckbjones/ppmread.c

Last active December 16, 2015 05:29
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ppmread - display a pgma or ppm file using OpenGL.
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ppmread.c
/*****************************************************************************
* Charles Jones
* 2013-04-14
* ppmread - display a pgma or ppm file using OpenGL
*****************************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif
#define BUF_SZ 70
/**
Structure for holding information about the PGMA file.
*/
typedef struct _pgma_t {
int type; // 2 = PGMA. 3 = PPM
int width;
int height;
int size; // width * height
int max_level;
float scale;
GLuint *pixels;
} pgma_t;
pgma_t pgma;
/**
Intermediate function called by parse_pgma().
Copies the given string into the appropriate
field in the given pgma structure.
Also allocates the memory needed to store
each pixel value in the structure,
which must be freed by free_pgma().
*/
static int state = 0;
void parse_pgma_field(pgma_t* pgma, char* field) {
static int row, col;
//printf(stderr, "state = %d. i = %d, j = %d. field = '%s'\n", state, i, j, field);
if (strlen(field) <= 0) {
return;
}
switch(state) {
case 0: // start of file;
if (strcmp(field, "P2") == 0) {
pgma->type = 2;
} else if (strcmp(field, "P3") == 0) {
pgma->type = 3;
} else {
fprintf(stderr, "Input file not PGMA or PPM!\n");
exit(1);
}
++state;
break;
case 1: //width
pgma->width = atoi(field);
++state;
break;
case 2: //height.
pgma->height = atoi(field);
pgma->size = pgma->width * pgma->height;
// at this point we can create the array for the pixels
pgma->pixels = (GLuint*)malloc(3 * sizeof(GLuint) * pgma->size);
row = pgma->height - 1;
col = 0;
++state;
break;
case 3: //max_level
pgma->max_level = atoi(field);
pgma->scale = 255.0 / pgma->max_level;
++state;
break;
case 4: // red component of pixel
pgma->pixels[3*(row*pgma->width + col)] = atoi(field);
if (pgma->type == 2) {
pgma->pixels[3*(row*pgma->width + col)+1] = atoi(field);
pgma->pixels[3*(row*pgma->width + col)+2] = atoi(field);
if(++col >= pgma->width) {
row -= 1;
col = 0;
}
} else { // type == 3
++state;
}
break;
case 5: // green component of pixel
pgma->pixels[3*(row*pgma->width + col)+1] = atoi(field);
++state;
break;
case 6: // blue component of pixel
pgma->pixels[3*(row*pgma->width + col)+2] = atoi(field);
if(++col >= pgma->width) {
row -= 1;
col = 0;
}
state = 4;
break;
}
}
/**
Reads pgma image data from the given FILE stream
and populates the given pgma structure with it.
*/
void parse_pgma(pgma_t* pgma, FILE* file) {
// read from file into struct
int cnt = 0, len = 0;
char buf[1 + 1], field[BUF_SZ + 1];
state = 0
while(fgets(buf, 2, file)) {
// if (cnt++ % 100 * 1024 == 0) {
// fprintf(stderr, "read %d bytes.\n", cnt);
// }
if (isspace(*buf) || *buf == '#') {
//skip comments
if (*buf == '#') {
// fprintf(stderr, "got comment.\n");
while(fgets(buf, 2, file) && *buf != '\n');
}
// fprintf(stderr, "got field: '%*.*s'\n", len, len, field);
// parse field, then clear buffer for next field
field[len] = 0;
parse_pgma_field(pgma, field);
len = 0;
} else {
field[len++] = *buf;
if (len == BUF_SZ) {
fprintf(stderr, "Read more than 70 bytes: '%*.*s", BUF_SZ, BUF_SZ, field);
exit(1);
}
}
}
//eof. parse last field, if any
field[len] = 0;
parse_pgma_field(pgma, field);
fprintf(stderr, "EOF. read %d bytes.\n", cnt);
}
/**
Frees the memory allocated by parse_pgma() to
store each pixel value in the image data.
*/
void free_pgma(pgma_t* pgma) {
free(pgma->pixels);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glRasterPos2i(0,0);
glDrawPixels(pgma.width, pgma.height, GL_RGB, GL_UNSIGNED_INT, pgma.pixels);
glFlush();
printf("finished display \n");
}
void myreshape(int h, int w)
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLfloat) pgma.width, 0.0, (GLfloat) pgma.height);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glViewport(0,0,h,w);
}
/**
Read a pgma image from the given file, process the data,
write the distortion and rate to stdout and
write the encoded, reconstructed, and error images back out to new files.
*/
int main(int argc, char **argv) {
FILE *infile;
if (argc < 2) {
fprintf(stderr, "missing filename\n");
exit(1);
}
printf("Displaying image from %s\n", argv[1]);
// parse pgma from infile
infile = fopen(argv[1], "r");
parse_pgma(&pgma, infile);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB );
glutInitWindowSize(pgma.width, pgma.height);
glutInitWindowPosition(0,0);
glutCreateWindow("image");
glutReshapeFunc(myreshape);
glutDisplayFunc(display);
glPixelTransferf(GL_RED_SCALE, pgma.scale);
glPixelTransferf(GL_GREEN_SCALE, pgma.scale);
glPixelTransferf(GL_BLUE_SCALE, pgma.scale);
glPixelStorei(GL_UNPACK_SWAP_BYTES,GL_TRUE);
glClearColor(1.0, 1.0, 1.0, 1.0);
glutMainLoop();
return 0;
}
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