gunslinger/source/graphics/gs_camera.c

#include "graphics/gs_camera.h"
#include "platform/gs_platform.h"
#include "base/gs_engine.h"

gs_vec3 gs_camera_forward( gs_camera* cam )
{
	return ( gs_quat_rotate( cam->transform.rotation, ( gs_vec3 ){ 0.0f, 0.0f, -1.0f } ) );
} 

gs_vec3 gs_camera_backward( gs_camera* cam )
{
	return ( gs_quat_rotate( cam->transform.rotation, ( gs_vec3 ){ 0.0f, 0.0f, 1.0f } ) );
} 

gs_vec3 gs_camera_up( gs_camera* cam )
{
	return ( gs_quat_rotate( cam->transform.rotation, ( gs_vec3 ){ 0.0f, 1.0f, 0.0f } ) );
}

gs_vec3 gs_camera_down( gs_camera* cam )
{
	return ( gs_quat_rotate( cam->transform.rotation, ( gs_vec3 ){ 0.0f, -1.0f, 0.0f } ) );
}

gs_vec3 gs_camera_right( gs_camera* cam )
{
	return ( gs_quat_rotate( cam->transform.rotation, ( gs_vec3 ){ 1.0f, 0.0f, 0.0f } ) );
}

gs_vec3 gs_camera_left( gs_camera* cam )
{
	return ( gs_quat_rotate( cam->transform.rotation, ( gs_vec3 ){ -1.0f, 0.0f, 0.0f } ) );
}

gs_vec3 gs_camera_unproject( gs_camera* cam, gs_vec3 coords, s32 view_width, s32 view_height )
{
	gs_vec3 wc = {0};

	// Get inverse of view projection from camera
	gs_mat4 inverse_vp = gs_mat4_inverse( gs_camera_get_view_projection( cam, view_width, view_height ) );	

	f32 w_x = (f32)coords.x;
	f32 w_y = (f32)coords.y;
	f32 w_z = (f32)coords.z;

	// Transform from ndc
	gs_vec4 in;
	in.x = (w_x / (f32)view_width ) * 2.f - 1.f;
	in.y = 1.f - (w_y / (f32)view_height) * 2.f;
	in.z = 2.f * w_z - 1.f;
	in.w = 1.f;

	// To world coords
	gs_vec4 out = gs_mat4_mul_vec4( inverse_vp, in );
	if ( out.w == 0.f )
	{
		// Avoid div by zero
		return wc;
	}

	out.w = 1.f / out.w;
	wc = (gs_vec3) {
		out.x * out.w,
		out.y * out.w,
		out.z * out.w
	};

	return wc;
}

gs_mat4 gs_camera_get_view_projection( gs_camera* cam, s32 view_width, s32 view_height )
{
	gs_mat4 view = gs_camera_get_view( cam );
	gs_mat4 proj = gs_camera_get_projection( cam, view_width, view_height );
	return gs_mat4_mul( proj, view );	
}

gs_mat4 gs_camera_get_view( gs_camera* cam )
{
	gs_vec3 up = gs_camera_up( cam );
	gs_vec3 forward = gs_camera_forward( cam );
	gs_vec3 target = gs_vec3_add( forward, cam->transform.position );
	return gs_mat4_look_at( cam->transform.position, target, up );
}

gs_mat4 gs_camera_get_projection( gs_camera* cam, s32 view_width, s32 view_height )
{
	gs_mat4 proj_mat = gs_mat4_identity();

	switch( cam->proj_type )
	{
		case gs_projection_type_perspective:
		{
			proj_mat = gs_mat4_perspective( cam->fov, (f32)view_width / (f32)view_height, cam->near_plane, cam->far_plane );
		} break;

		case gs_projection_type_orthographic:
		{
			f32 _ar = (f32)view_width / (f32)view_height;
			f32 distance = 0.5f * ( cam->far_plane - cam->near_plane );
			const f32 ortho_scale = cam->ortho_scale;
			const f32 aspect_ratio = _ar;
			proj_mat = gs_mat4_ortho
			(
				-ortho_scale * aspect_ratio, 
				ortho_scale * aspect_ratio, 
				-ortho_scale, 
				ortho_scale, 
				-distance, 
				distance	
			);
			// (
			// 	0.f, 
			// 	view_width, 
			// 	view_height, 
			// 	0.f, 
			// 	cam->near_plane, 
			// 	cam->far_plane	
			// );
		} break;
	}

	return proj_mat;
}

void gs_camera_offset_orientation( gs_camera* cam, f32 yaw, f32 pitch )
{
	gs_quat x = gs_quat_angle_axis(gs_deg_to_rad(yaw), (gs_vec3){0.f, 1.f, 0.f});		// Absolute up
	gs_quat y = gs_quat_angle_axis(gs_deg_to_rad(pitch), gs_camera_right(cam));			// Relative right
	cam->transform.rotation = gs_quat_mul(gs_quat_mul(x, y), cam->transform.rotation);
}