OpenGL code to rotate, translate and scale a rectangle using basic matrix transforms, written in C.

translate_rotate_scale.c

//
// Created by vishal on 11/1/17.
//

#include <GL/glut.h>

#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

typedef struct {
    GLfloat x, y;
} Point;

const Point sqr[] = {
        {20,  30},
        {20,  80},
        {100, 80},
        {100, 30}
};

GLfloat tr_matrix[][3] = {
        {1, 0, 200},
        {0, 1, 10},
        {0, 0, 1}
};

GLfloat sc_matrix[][3] = {
        {2, 0, 0},
        {0, 3, 0},
        {0, 0, 1}
};

//sin45 = 0.707
GLfloat rt_matrix[][3] = {
        {0.707, -0.707f, 0},
        {0.707, 0.707,   0},
        {0,     0,       1}
};

Point multiply(GLfloat m[][3], Point v) {

    GLfloat arr[] = {v.x, v.y, 1}, ans[] = {0, 0, 1};
    int i, j;
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            ans[i] += m[i][j] * arr[j];
        }
    }
    Point p = {ans[0], ans[1]};
    return p;
}

void init_graph(int argc, char **argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(SCREEN_WIDTH, SCREEN_HEIGHT);
    glutCreateWindow(argv[0]);
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glPointSize(1.0f);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT);
}

void close_graph() {
    glutMainLoop();
}

void init() {
    glClear(GL_COLOR_BUFFER_BIT);
    const int xshift = 300;
    const int yshift = 300;
    //original
    glColor3f(0.5, 0.5, 0.5);
    glBegin(GL_LINE_LOOP);
    for (int i = 0; i < 4; ++i) {
        glVertex2f(sqr[i].x, sqr[i].y);
    }
    glEnd();

    //translated
    glColor3f(1, 0, 0);
    glBegin(GL_LINE_LOOP);
    for (int j = 0; j < 4; ++j) {
        Point p = multiply(tr_matrix, sqr[j]);
        glVertex2f(p.x, p.y);
    }
    glEnd();

    //scaled
    glColor3f(0, 1, 0);
    glBegin(GL_LINE_LOOP);
    for (int k = 0; k < 4; ++k) {
        Point p = multiply(sc_matrix, sqr[k]);
        glVertex2f(xshift + p.x, p.y);
    }
    glEnd();

    //rotated
    glColor3f(0, 0, 1);
    glBegin(GL_LINE_LOOP);
    for (int l = 0; l < 4; ++l) {
        Point p = multiply(rt_matrix, sqr[l]);
        glVertex2f(xshift/2 + p.x, yshift/2 + p.y);
    }
    glEnd();
    glFlush();
}

int main(int argc, char **argv) {
    init_graph(argc, argv);
    glutDisplayFunc(init);
    close_graph();
    return EXIT_SUCCESS;
}

trs_img.png

thanks very much that's help me❤️❤️❤️❤️