functions.c

This example shows how to create screens and plot an draw on them. It has been used to generate the two first figures of the documentation as well as a plot of the same sin(x) and x*sin(x) using lines instead of points.

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <math.h>

#include "mgsLib.h"

void adjustFunction(unsigned int *points, int nPpoints, int maxValY, double xMin, double xMax, double yMin, double yMax, double (*func)(double));

double xsin(double x);

int main()
{
    int scr, scr2, i;
    int vector[800];
    
    // Create a demo screen
    if ((scr = mgsCreateScreen(800, 600, "800 x 600 Screen", 0x204020, NULL)) < 0)
        exit(EXIT_FAILURE);
    
    // Draw two arrows to show height and width
    mgsLine(scr, 5, 80, 795, 80, 3, MGS_CWHITE);
    mgsLine(scr, 80, 5, 80, 595, 3, MGS_CWHITE);
    mgsRegPolygonVC(scr, 3, 80, 0, 80, 9, MGS_CWHITE);
    mgsRegPolygonVC(scr, 3, 80, 599, 80, 590, MGS_CWHITE);
    mgsRegPolygonVC(scr, 3, 0, 80, 9, 80, MGS_CWHITE);
    mgsRegPolygonVC(scr, 3, 799, 80, 790, 80, MGS_CWHITE);
    
    // Fit the text size and write the corner coordinates
    mgsSetFont(scr, 20, 0xFFC0C0, MGS_TRANSPARENT);
    mgsPuts(scr, 5, 5, "(0, 0)");
    mgsPuts(scr, 5, 577, "(0, 599)");
    mgsPuts(scr, 735, 5, "(799, 0)");
    mgsPuts(scr, 718, 577, "(799, 599)");
    
    // Fit the text size and write the height and width
    mgsSetFont(scr, 30, 0xFFA0A0, MGS_TRANSPARENT);
    mgsPuts(scr, 380, 88, "800");
    mgsPuts(scr, 90, 286, "600");
    
    // Show the created image
    mgsUpdateScreen(scr);
    
    // Go to the next stage after pressing S
    puts("Press S to continue");
    while(!mgsKeyPressed('S'));
    
    // Destroy the first demo screen
    mgsDeleteScreen(scr);
    
    // Create two new screens to plot the functions
    if ((scr = mgsCreateScreen(800, 600, "mgsLib Demo - Using Points", mgsRGBColor(200, 255, 200), NULL)) < 0)
        exit(EXIT_FAILURE);
    if ((scr2 = mgsCreateScreen(800, 600, "mgsLib Demo - Using Lines", mgsRGBColor(200, 200, 255), NULL)) < 0)
        exit(EXIT_FAILURE);
    
    // Draw the x and y axis on both screens
    mgsLine(scr, 0, 299, 800, 299, 4, MGS_CGREEN);
    mgsLine(scr, 399, 0, 399, 600, 4, MGS_CGREEN);
    mgsLine(scr2, 0, 299, 800, 299, 4, MGS_CGREEN);
    mgsLine(scr2, 399, 0, 399, 600, 4, MGS_CGREEN);

    // Calculate the values for sin(x) between -10.,0 and 10.0 an
    // adjusted (y axis) between -1.1 and 1.1
    adjustFunction(vector, 800, 600, -10.0, 10.0, -1.1, 1.1, sin);
    
    // Plot the points on one screen
    for(i = 0; i < 800; i++)
        mgsPoint(scr, i, vector[i], MGS_CBLUE);
    
    // and draw lines on the other
    for(i = 1; i < 800; i++)
        mgsLine(scr2, i - 1, vector[i - 1], i, vector[i], 1, MGS_CBLUE);
    
    // Calculate the values for x*sin(x) between -10.,0 and 10.0 an
    // adjusted (y axis) between -10.1 and 10.1
    adjustFunction(vector, 800, 600, -10.0, 10.0, -10.1, 10.1, xsin);
    
    // Plot the points on one screen
    for(i = 0; i < 800; i++)
        mgsPoint(scr, i, vector[i], MGS_CRED);
    
    // and draw lines on the other
    for(i = 1; i < 800; i++)
        mgsLine(scr2, i - 1, vector[i - 1], i, vector[i], 1, MGS_CRED);
    puts("\nDrawing x * sin(x)\n");
    puts("Drawing sin(x)\n");
    
    // Update both screens 
    mgsUpdateScreen(scr);
    mgsUpdateScreen(scr2);
    
    // And wait for S to be first released -remember we pressed it before-
    // and then pressed to exit.
    while(mgsKeyPressed('S'));
    puts("Press S to continue");
    while(!mgsKeyPressed('S'));
}

// Adjust a funcion defined on an interval to the screen coordinates and width(nPoints) and height(maxValY)
void adjustFunction(unsigned int *points, int nPoints, int maxValY, double xMin, double xMax, double yMin, double yMax, double (*func)(double))
{
    int i;
    double x, y, xdif, ydif;
    
    // We calculate the intervals once. We adjust input from 0, nPoints - 1 to xMin, xMax 
    // and output from yMin, yMax to maxValY - 1, 0
    maxValY --;
    nPoints--;
    xdif = xMax - xMin;
    ydif = yMax - yMin;
    for (i = 0; i <= nPoints; i++) {
        // Calculate the x corresponding to each i
        x = xMin + (double)i  * xdif / (double)nPoints;
        // Calculate y = f(x) where f is the given function 
        y = func(x);
        // Calculate the ploting value corresponding to y
        points[i] = maxValY - (y - yMin) * (double)maxValY / ydif;
    }
}

// Simply the x * sin(x) function
double xsin(double x)
{
    return x * sin(x);
}