2019/05/01 3D,C,Coding
We will add an other rectangle, shadow and animated camera in this part.
To use an arbitrary number of rectangles we will need a rectangle structure and an array that holds them. A rectangle is defined by it’s base point, side point and it’s normal vector. We will pre-calculate the width and height of the rectangle. We need members for transparency, diffuse and specular color also.
#include <stdio.h>
typedef struct
{
v3_t base_p;
v3_t side_p;
v3_t norm_v;
float wth;
float hth;
float transparency_c;
uint32v_t col_diff_u;
uint32_t col_spec_u;
} rect_t;
int rect_cnt_i = 2;
rect_t rectangles[ 2 ];
With this we can organize intersection detection to a separate function that returns the nearest rect intersecting with the given line.
#include <stdio.h>
nearest_res_t get_nearest_rect( v3_t start_p , v3_t end_p , rect_t* exclude_r )
{
nearest_res_t result = { 0 };
float dist_f = FLT_MAX;
if ( rect_cnt_i > 0 )
{
// iterate through all rectangles
for ( int index_r = 0 ; index_r < rect_cnt_i ; index_r ++ )
{
rect_t* rect = &rectangles[ index_r ];
if ( rect == exclude_r ) continue;
// project ray from camera focus point through window grid point to square plane
v3_t isect_p = line_plane_intersection( start_p , end_p , rect->base_p , rect->norm_v );
if ( isect_p.x != FLT_MAX )
{
// let's find if intersection point is in the rectangle
v3_t proj_p = point_line_projection( rect->side_p , rect->base_p , isect_p );
// check x and y distance of intersection point from square center
float dist_x = v3_length_squared( v3_sub( proj_p , rect->base_p ) );
float dist_y = v3_length_squared( v3_sub( proj_p , isect_p ) );
// compare squared distances with squared distances of rectangle
if ( dist_x < ( rect->wth / 2.0 ) * ( rect->wth / 2.0 ) &&
dist_y < ( rect->hth / 2.0 ) * ( rect->hth / 2.0 ) )
{
// cross point is inside square, let's calculate it's color based on light reflection angle
float distance = v3_length_squared( v3_sub( isect_p , start_p ) );
if ( distance < dist_f )
{
result.rect = rect;
result.isect_p = isect_p;
dist_f = distance;
}
}
}
}
}
return result;
}
To introduce shadows we need to modify the window grid iteration loop a little. If there is an obstacle ( rectangle ) between the intersection point and the light we set that point to the shadow color, if not we calculate diffuse and specular color.
#include <stdio.h>
// create rays going through the camera window quad starting from the top left corner
for ( int row_i = 0 ; row_i < grid_rows_i ; row_i++ )
{
for ( int col_i = 0 ; col_i < grid_cols_i ; col_i++ )
{
v3_t window_grid_v = camera_target_p;
window_grid_v = v3_add( window_grid_v , v3_scale( window_stepx_v , grid_cols_i / 2 - col_i ) );
window_grid_v = v3_add( window_grid_v , v3_scale( window_stepy_v , - grid_rows_i / 2 + row_i ) );
// ray/pixel location on screen
int screen_grid_x = screen_step_size_f * col_i;
int screen_grid_y = screen_step_size_f * row_i;
// check for intersection
uint32_t color = 0x000000FF; // background color
nearest_res_t result = get_nearest_rect( camera_focus_p , window_grid_v , NULL );
if ( result.rect != NULL )
{
// check for direct connection with light for diffuse color
nearest_res_t blocker_r = get_nearest_rect( result.isect_p , light_p , result.rect );
if ( blocker_r.rect == NULL )
{
// diffuse color
color = result.rect->col_diff_u;
// specular color
// mirror light point on normal vector to get perfect reflection
v3_t light_mirr_p = point_line_mirror( result.isect_p , v3_add( result.isect_p , result.rect->norm_v ) , light_p );
v3_t tofocus = v3_sub( camera_focus_p , result.isect_p );
v3_t tomirrored = v3_sub( light_mirr_p , result.isect_p );
float angle = v3_angle( tomirrored , tofocus );
// the smaller the angle the closer the mirrored ray and the real ray are - reflection
float colorsp_f = ( float ) 0xFF * ( ( M_PI - angle ) / M_PI );
uint32_t colorsp_u = ( uint8_t ) colorsp_f;
colorsp_u = colorsp_u << 24 | colorsp_u << 16 | colorsp_u << 8 | 0xFF;
color = color_average( color , colorsp_u );
}
else
{
// shadow
color = 0x111111FF;
}
// if rect is transparent calculate refraction and check for further intersections
// reflect ray on intersection point and check for further intersections
}
framebuffer_drawsquare( screen_grid_x , screen_grid_y , screen_step_size_f , color );
}
}
Finally let’s make the camera movable with the arrow keys. Let’s put the whole grid iteration in an infinite loop and check for keypress in every iteration.
#include <stdio.h>
int code = getch( );
if ( code == 67 ) camera_focus_p.x += 10.0;
if ( code == 68 ) camera_focus_p.x -= 10.0;
Final result :
Download the code : raytrace_part_three.c