Draw bar chart (university homework - libgd)

bar_chart.c

// author: Maciej Ciemborowicz
// Jagiellonian University
// ZGK 2011/2012

#include <gd.h>
#include <gdfontg.h>
#include <string.h>
#include "gd_wewy.h"

int main(int argc, char * argv[])
{
  
  if (argc < 2) {
    fprintf(stderr, "Error: No argument!\n");
    return 1;
  }
  
  typedef struct Chart {
    int height, width, pos_x, pos_y;
  } Chart;
  
  gdImagePtr img;
  int a, bar_color, font_color, highest_val, space_width, bar_width, x, y;
  Chart chart;
  
  //////////////////////////////////////////////////////////////////////
  
  img = gdImageCreateTrueColor(800, 400);
  bar_color = gdTrueColor(200, 120, 30);
  font_color = gdTrueColor(255, 255, 255);
  chart.height = gdImageSY(img) - 100;
  chart.width = gdImageSX(img) - 100;
  chart.pos_x = 50;
  chart.pos_y = 50;
  
  space_width = (chart.width / (argc - 1)) * 0.3;
  bar_width = ((chart.width - ((argc - 2) * space_width)) / (argc - 1));

  //////////////////////////////////////////////////////////////////////
  // find highest value and validate data
  
  for (a=1; a<argc; ++a) {

    int val;

    if ((val = atoi(argv[a])) && 0 <= val) {
      if (highest_val < val)
        highest_val = val;
    }
    else {
      fprintf(stderr, "Error: %d (%d) unsupported argument!\n", a, val);
      return 1;
    }
    
  }

  //////////////////////////////////////////////////////////////////////
  // draw chart
  
  x = chart.pos_x;
  y = 0;
  
  for (a=1; a<argc; ++a) {
    
    int val = atoi(argv[a]);
    char string[20];
    int bar_height = gdImageSY(img) - chart.pos_y - ((val * chart.height) / highest_val);    
    gdFontPtr font = gdFontGetGiant();
    
    sprintf(string, "%d", a);

    // draw bar
    gdImageFilledRectangle(img, 
                           x, 
                           gdImageSY(img) - chart.pos_y, 
                           x + bar_width, 
                           bar_height , 
                           bar_color);
    
    // draw argument
    gdImageString(img, 
                  font, 
                  x + (bar_width/2) - (strlen(string) * font->w) / 2, 
                  gdImageSY(img) - (chart.pos_y / 2) - (font->h / 2), 
                  string, 
                  font_color);
    
    // draw value
    gdImageString(img, 
                  font, 
                  x + (bar_width/2) - (strlen(argv[a]) * font->w) / 2, 
                  bar_height - 32, 
                  argv[a], 
                  font_color);
  
    x += bar_width + space_width;
    
  }
  
  zapiszPng(img, "wynik.png");
  gdImageDestroy(img);

  return 0;
}