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A multi-platform library for OpenGL, OpenGL ES, Vulkan, window and input
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glfw/examples/boing.c

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/*****************************************************************************
* Title: GLBoing
* Desc: Tribute to Amiga Boing.
* Author: Jim Brooks <gfx@jimbrooks.org>
* Original Amiga authors were R.J. Mical and Dale Luck.
* GLFW conversion by Marcus Geelnard
* Notes: - 360' = 2*PI [radian]
*
* - Distances between objects are created by doing a relative
* Z translations.
*
* - Although OpenGL enticingly supports alpha-blending,
* the shadow of the original Boing didn't affect the color
* of the grid.
*
* - [Marcus] Changed timing scheme from interval driven to frame-
* time based animation steps (which results in much smoother
* movement)
*
* History of Amiga Boing:
*
* Boing was demonstrated on the prototype Amiga (codenamed "Lorraine") in
* 1985. According to legend, it was written ad-hoc in one night by
* R. J. Mical and Dale Luck. Because the bouncing ball animation was so fast
* and smooth, attendees did not believe the Amiga prototype was really doing
* the rendering. Suspecting a trick, they began looking around the booth for
* a hidden computer or VCR.
*****************************************************************************/
#if defined(_MSC_VER)
// Make MS math.h define M_PI
#define _USE_MATH_DEFINES
#endif
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <linmath.h>
/*****************************************************************************
* Various declarations and macros
*****************************************************************************/
/* Prototypes */
void init( void );
void display( void );
void reshape( GLFWwindow* window, int w, int h );
void key_callback( GLFWwindow* window, int key, int scancode, int action, int mods );
void mouse_button_callback( GLFWwindow* window, int button, int action, int mods );
void cursor_position_callback( GLFWwindow* window, double x, double y );
void DrawBoingBall( void );
void BounceBall( double dt );
void DrawBoingBallBand( GLfloat long_lo, GLfloat long_hi );
void DrawGrid( void );
#define RADIUS 70.f
#define STEP_LONGITUDE 22.5f /* 22.5 makes 8 bands like original Boing */
#define STEP_LATITUDE 22.5f
#define DIST_BALL (RADIUS * 2.f + RADIUS * 0.1f)
#define VIEW_SCENE_DIST (DIST_BALL * 3.f + 200.f)/* distance from viewer to middle of boing area */
#define GRID_SIZE (RADIUS * 4.5f) /* length (width) of grid */
#define BOUNCE_HEIGHT (RADIUS * 2.1f)
#define BOUNCE_WIDTH (RADIUS * 2.1f)
#define SHADOW_OFFSET_X -20.f
#define SHADOW_OFFSET_Y 10.f
#define SHADOW_OFFSET_Z 0.f
#define WALL_L_OFFSET 0.f
#define WALL_R_OFFSET 5.f
/* Animation speed (50.0 mimics the original GLUT demo speed) */
#define ANIMATION_SPEED 50.f
/* Maximum allowed delta time per physics iteration */
#define MAX_DELTA_T 0.02f
/* Draw ball, or its shadow */
typedef enum { DRAW_BALL, DRAW_BALL_SHADOW } DRAW_BALL_ENUM;
/* Vertex type */
typedef struct {float x; float y; float z;} vertex_t;
/* Global vars */
int windowed_xpos, windowed_ypos, windowed_width, windowed_height;
int width, height;
GLfloat deg_rot_y = 0.f;
GLfloat deg_rot_y_inc = 2.f;
int override_pos = GLFW_FALSE;
GLfloat cursor_x = 0.f;
GLfloat cursor_y = 0.f;
GLfloat ball_x = -RADIUS;
GLfloat ball_y = -RADIUS;
GLfloat ball_x_inc = 1.f;
GLfloat ball_y_inc = 2.f;
DRAW_BALL_ENUM drawBallHow;
double t;
double t_old = 0.f;
double dt;
/* Random number generator */
#ifndef RAND_MAX
#define RAND_MAX 4095
#endif
/*****************************************************************************
* Truncate a degree.
*****************************************************************************/
GLfloat TruncateDeg( GLfloat deg )
{
if ( deg >= 360.f )
return (deg - 360.f);
else
return deg;
}
/*****************************************************************************
* Convert a degree (360-based) into a radian.
* 360' = 2 * PI
*****************************************************************************/
double deg2rad( double deg )
{
return deg / 360 * (2 * M_PI);
}
/*****************************************************************************
* 360' sin().
*****************************************************************************/
double sin_deg( double deg )
{
return sin( deg2rad( deg ) );
}
/*****************************************************************************
* 360' cos().
*****************************************************************************/
double cos_deg( double deg )
{
return cos( deg2rad( deg ) );
}
/*****************************************************************************
* Compute a cross product (for a normal vector).
*
* c = a x b
*****************************************************************************/
void CrossProduct( vertex_t a, vertex_t b, vertex_t c, vertex_t *n )
{
GLfloat u1, u2, u3;
GLfloat v1, v2, v3;
u1 = b.x - a.x;
u2 = b.y - a.y;
u3 = b.y - a.z;
v1 = c.x - a.x;
v2 = c.y - a.y;
v3 = c.z - a.z;
n->x = u2 * v3 - v2 * v3;
n->y = u3 * v1 - v3 * u1;
n->z = u1 * v2 - v1 * u2;
}
#define BOING_DEBUG 0
/*****************************************************************************
* init()
*****************************************************************************/
void init( void )
{
/*
* Clear background.
*/
glClearColor( 0.55f, 0.55f, 0.55f, 0.f );
glShadeModel( GL_FLAT );
}
/*****************************************************************************
* display()
*****************************************************************************/
void display(void)
{
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glPushMatrix();
drawBallHow = DRAW_BALL_SHADOW;
DrawBoingBall();
DrawGrid();
drawBallHow = DRAW_BALL;
DrawBoingBall();
glPopMatrix();
glFlush();
}
/*****************************************************************************
* reshape()
*****************************************************************************/
void reshape( GLFWwindow* window, int w, int h )
{
mat4x4 projection, view;
glViewport( 0, 0, (GLsizei)w, (GLsizei)h );
glMatrixMode( GL_PROJECTION );
mat4x4_perspective( projection,
2.f * (float) atan2( RADIUS, 200.f ),
(float)w / (float)h,
1.f, VIEW_SCENE_DIST );
glLoadMatrixf((const GLfloat*) projection);
glMatrixMode( GL_MODELVIEW );
{
vec3 eye = { 0.f, 0.f, VIEW_SCENE_DIST };
vec3 center = { 0.f, 0.f, 0.f };
vec3 up = { 0.f, -1.f, 0.f };
mat4x4_look_at( view, eye, center, up );
}
glLoadMatrixf((const GLfloat*) view);
}
void key_callback( GLFWwindow* window, int key, int scancode, int action, int mods )
{
if (action != GLFW_PRESS)
return;
if (key == GLFW_KEY_ESCAPE && mods == 0)
glfwSetWindowShouldClose(window, GLFW_TRUE);
if ((key == GLFW_KEY_ENTER && mods == GLFW_MOD_ALT) ||
(key == GLFW_KEY_F11 && mods == GLFW_MOD_ALT))
{
if (glfwGetWindowMonitor(window))
{
glfwSetWindowMonitor(window, NULL,
windowed_xpos, windowed_ypos,
windowed_width, windowed_height, 0);
}
else
{
GLFWmonitor* monitor = glfwGetPrimaryMonitor();
if (monitor)
{
const GLFWvidmode* mode = glfwGetVideoMode(monitor);
glfwGetWindowPos(window, &windowed_xpos, &windowed_ypos);
glfwGetWindowSize(window, &windowed_width, &windowed_height);
glfwSetWindowMonitor(window, monitor, 0, 0, mode->width, mode->height, mode->refreshRate);
}
}
}
}
static void set_ball_pos ( GLfloat x, GLfloat y )
{
ball_x = (width / 2) - x;
ball_y = y - (height / 2);
}
void mouse_button_callback( GLFWwindow* window, int button, int action, int mods )
{
if (button != GLFW_MOUSE_BUTTON_LEFT)
return;
if (action == GLFW_PRESS)
{
override_pos = GLFW_TRUE;
set_ball_pos(cursor_x, cursor_y);
}
else
{
override_pos = GLFW_FALSE;
}
}
void cursor_position_callback( GLFWwindow* window, double x, double y )
{
cursor_x = (float) x;
cursor_y = (float) y;
if ( override_pos )
set_ball_pos(cursor_x, cursor_y);
}
/*****************************************************************************
* Draw the Boing ball.
*
* The Boing ball is sphere in which each facet is a rectangle.
* Facet colors alternate between red and white.
* The ball is built by stacking latitudinal circles. Each circle is composed
* of a widely-separated set of points, so that each facet is noticably large.
*****************************************************************************/
void DrawBoingBall( void )
{
GLfloat lon_deg; /* degree of longitude */
double dt_total, dt2;
glPushMatrix();
glMatrixMode( GL_MODELVIEW );
/*
* Another relative Z translation to separate objects.
*/
glTranslatef( 0.0, 0.0, DIST_BALL );
/* Update ball position and rotation (iterate if necessary) */
dt_total = dt;
while( dt_total > 0.0 )
{
dt2 = dt_total > MAX_DELTA_T ? MAX_DELTA_T : dt_total;
dt_total -= dt2;
BounceBall( dt2 );
deg_rot_y = TruncateDeg( deg_rot_y + deg_rot_y_inc*((float)dt2*ANIMATION_SPEED) );
}
/* Set ball position */
glTranslatef( ball_x, ball_y, 0.0 );
/*
* Offset the shadow.
*/
if ( drawBallHow == DRAW_BALL_SHADOW )
{
glTranslatef( SHADOW_OFFSET_X,
SHADOW_OFFSET_Y,
SHADOW_OFFSET_Z );
}
/*
* Tilt the ball.
*/
glRotatef( -20.0, 0.0, 0.0, 1.0 );
/*
* Continually rotate ball around Y axis.
*/
glRotatef( deg_rot_y, 0.0, 1.0, 0.0 );
/*
* Set OpenGL state for Boing ball.
*/
glCullFace( GL_FRONT );
glEnable( GL_CULL_FACE );
glEnable( GL_NORMALIZE );
/*
* Build a faceted latitude slice of the Boing ball,
* stepping same-sized vertical bands of the sphere.
*/
for ( lon_deg = 0;
lon_deg < 180;
lon_deg += STEP_LONGITUDE )
{
/*
* Draw a latitude circle at this longitude.
*/
DrawBoingBallBand( lon_deg,
lon_deg + STEP_LONGITUDE );
}
glPopMatrix();
return;
}
/*****************************************************************************
* Bounce the ball.
*****************************************************************************/
void BounceBall( double delta_t )
{
GLfloat sign;
GLfloat deg;
if ( override_pos )
return;
/* Bounce on walls */
if ( ball_x > (BOUNCE_WIDTH/2 + WALL_R_OFFSET ) )
{
ball_x_inc = -0.5f - 0.75f * (GLfloat)rand() / (GLfloat)RAND_MAX;
deg_rot_y_inc = -deg_rot_y_inc;
}
if ( ball_x < -(BOUNCE_HEIGHT/2 + WALL_L_OFFSET) )
{
ball_x_inc = 0.5f + 0.75f * (GLfloat)rand() / (GLfloat)RAND_MAX;
deg_rot_y_inc = -deg_rot_y_inc;
}
/* Bounce on floor / roof */
if ( ball_y > BOUNCE_HEIGHT/2 )
{
ball_y_inc = -0.75f - 1.f * (GLfloat)rand() / (GLfloat)RAND_MAX;
}
if ( ball_y < -BOUNCE_HEIGHT/2*0.85 )
{
ball_y_inc = 0.75f + 1.f * (GLfloat)rand() / (GLfloat)RAND_MAX;
}
/* Update ball position */
ball_x += ball_x_inc * ((float)delta_t*ANIMATION_SPEED);
ball_y += ball_y_inc * ((float)delta_t*ANIMATION_SPEED);
/*
* Simulate the effects of gravity on Y movement.
*/
if ( ball_y_inc < 0 ) sign = -1.0; else sign = 1.0;
deg = (ball_y + BOUNCE_HEIGHT/2) * 90 / BOUNCE_HEIGHT;
if ( deg > 80 ) deg = 80;
if ( deg < 10 ) deg = 10;
ball_y_inc = sign * 4.f * (float) sin_deg( deg );
}
/*****************************************************************************
* Draw a faceted latitude band of the Boing ball.
*
* Parms: long_lo, long_hi
* Low and high longitudes of slice, resp.
*****************************************************************************/
void DrawBoingBallBand( GLfloat long_lo,
GLfloat long_hi )
{
vertex_t vert_ne; /* "ne" means south-east, so on */
vertex_t vert_nw;
vertex_t vert_sw;
vertex_t vert_se;
vertex_t vert_norm;
GLfloat lat_deg;
static int colorToggle = 0;
/*
* Iterate thru the points of a latitude circle.
* A latitude circle is a 2D set of X,Z points.
*/
for ( lat_deg = 0;
lat_deg <= (360 - STEP_LATITUDE);
lat_deg += STEP_LATITUDE )
{
/*
* Color this polygon with red or white.
*/
if ( colorToggle )
glColor3f( 0.8f, 0.1f, 0.1f );
else
glColor3f( 0.95f, 0.95f, 0.95f );
#if 0
if ( lat_deg >= 180 )
if ( colorToggle )
glColor3f( 0.1f, 0.8f, 0.1f );
else
glColor3f( 0.5f, 0.5f, 0.95f );
#endif
colorToggle = ! colorToggle;
/*
* Change color if drawing shadow.
*/
if ( drawBallHow == DRAW_BALL_SHADOW )
glColor3f( 0.35f, 0.35f, 0.35f );
/*
* Assign each Y.
*/
vert_ne.y = vert_nw.y = (float) cos_deg(long_hi) * RADIUS;
vert_sw.y = vert_se.y = (float) cos_deg(long_lo) * RADIUS;
/*
* Assign each X,Z with sin,cos values scaled by latitude radius indexed by longitude.
* Eg, long=0 and long=180 are at the poles, so zero scale is sin(longitude),
* while long=90 (sin(90)=1) is at equator.
*/
vert_ne.x = (float) cos_deg( lat_deg ) * (RADIUS * (float) sin_deg( long_lo + STEP_LONGITUDE ));
vert_se.x = (float) cos_deg( lat_deg ) * (RADIUS * (float) sin_deg( long_lo ));
vert_nw.x = (float) cos_deg( lat_deg + STEP_LATITUDE ) * (RADIUS * (float) sin_deg( long_lo + STEP_LONGITUDE ));
vert_sw.x = (float) cos_deg( lat_deg + STEP_LATITUDE ) * (RADIUS * (float) sin_deg( long_lo ));
vert_ne.z = (float) sin_deg( lat_deg ) * (RADIUS * (float) sin_deg( long_lo + STEP_LONGITUDE ));
vert_se.z = (float) sin_deg( lat_deg ) * (RADIUS * (float) sin_deg( long_lo ));
vert_nw.z = (float) sin_deg( lat_deg + STEP_LATITUDE ) * (RADIUS * (float) sin_deg( long_lo + STEP_LONGITUDE ));
vert_sw.z = (float) sin_deg( lat_deg + STEP_LATITUDE ) * (RADIUS * (float) sin_deg( long_lo ));
/*
* Draw the facet.
*/
glBegin( GL_POLYGON );
CrossProduct( vert_ne, vert_nw, vert_sw, &vert_norm );
glNormal3f( vert_norm.x, vert_norm.y, vert_norm.z );
glVertex3f( vert_ne.x, vert_ne.y, vert_ne.z );
glVertex3f( vert_nw.x, vert_nw.y, vert_nw.z );
glVertex3f( vert_sw.x, vert_sw.y, vert_sw.z );
glVertex3f( vert_se.x, vert_se.y, vert_se.z );
glEnd();
#if BOING_DEBUG
printf( "----------------------------------------------------------- \n" );
printf( "lat = %f long_lo = %f long_hi = %f \n", lat_deg, long_lo, long_hi );
printf( "vert_ne x = %.8f y = %.8f z = %.8f \n", vert_ne.x, vert_ne.y, vert_ne.z );
printf( "vert_nw x = %.8f y = %.8f z = %.8f \n", vert_nw.x, vert_nw.y, vert_nw.z );
printf( "vert_se x = %.8f y = %.8f z = %.8f \n", vert_se.x, vert_se.y, vert_se.z );
printf( "vert_sw x = %.8f y = %.8f z = %.8f \n", vert_sw.x, vert_sw.y, vert_sw.z );
#endif
}
/*
* Toggle color so that next band will opposite red/white colors than this one.
*/
colorToggle = ! colorToggle;
/*
* This circular band is done.
*/
return;
}
/*****************************************************************************
* Draw the purple grid of lines, behind the Boing ball.
* When the Workbench is dropped to the bottom, Boing shows 12 rows.
*****************************************************************************/
void DrawGrid( void )
{
int row, col;
const int rowTotal = 12; /* must be divisible by 2 */
const int colTotal = rowTotal; /* must be same as rowTotal */
const GLfloat widthLine = 2.0; /* should be divisible by 2 */
const GLfloat sizeCell = GRID_SIZE / rowTotal;
const GLfloat z_offset = -40.0;
GLfloat xl, xr;
GLfloat yt, yb;
glPushMatrix();
glDisable( GL_CULL_FACE );
/*
* Another relative Z translation to separate objects.
*/
glTranslatef( 0.0, 0.0, DIST_BALL );
/*
* Draw vertical lines (as skinny 3D rectangles).
*/
for ( col = 0; col <= colTotal; col++ )
{
/*
* Compute co-ords of line.
*/
xl = -GRID_SIZE / 2 + col * sizeCell;
xr = xl + widthLine;
yt = GRID_SIZE / 2;
yb = -GRID_SIZE / 2 - widthLine;
glBegin( GL_POLYGON );
glColor3f( 0.6f, 0.1f, 0.6f ); /* purple */
glVertex3f( xr, yt, z_offset ); /* NE */
glVertex3f( xl, yt, z_offset ); /* NW */
glVertex3f( xl, yb, z_offset ); /* SW */
glVertex3f( xr, yb, z_offset ); /* SE */
glEnd();
}
/*
* Draw horizontal lines (as skinny 3D rectangles).
*/
for ( row = 0; row <= rowTotal; row++ )
{
/*
* Compute co-ords of line.
*/
yt = GRID_SIZE / 2 - row * sizeCell;
yb = yt - widthLine;
xl = -GRID_SIZE / 2;
xr = GRID_SIZE / 2 + widthLine;
glBegin( GL_POLYGON );
glColor3f( 0.6f, 0.1f, 0.6f ); /* purple */
glVertex3f( xr, yt, z_offset ); /* NE */
glVertex3f( xl, yt, z_offset ); /* NW */
glVertex3f( xl, yb, z_offset ); /* SW */
glVertex3f( xr, yb, z_offset ); /* SE */
glEnd();
}
glPopMatrix();
return;
}
/*======================================================================*
* main()
*======================================================================*/
int main( void )
{
GLFWwindow* window;
/* Init GLFW */
if( !glfwInit() )
exit( EXIT_FAILURE );
window = glfwCreateWindow( 400, 400, "Boing (classic Amiga demo)", NULL, NULL );
if (!window)
{
glfwTerminate();
exit( EXIT_FAILURE );
}
glfwSetWindowAspectRatio(window, 1, 1);
glfwSetFramebufferSizeCallback(window, reshape);
glfwSetKeyCallback(window, key_callback);
glfwSetMouseButtonCallback(window, mouse_button_callback);
glfwSetCursorPosCallback(window, cursor_position_callback);
glfwMakeContextCurrent(window);
gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
glfwSwapInterval( 1 );
glfwGetFramebufferSize(window, &width, &height);
reshape(window, width, height);
glfwSetTime( 0.0 );
init();
/* Main loop */
for (;;)
{
/* Timing */
t = glfwGetTime();
dt = t - t_old;
t_old = t;
/* Draw one frame */
display();
/* Swap buffers */
glfwSwapBuffers(window);
glfwPollEvents();
/* Check if we are still running */
if (glfwWindowShouldClose(window))
break;
}
glfwTerminate();
exit( EXIT_SUCCESS );
}