# HG changeset patch
# User John Tsiombikas <nuclear@member.fsf.org>
# Date 1422114575 -7200
# Node ID 64483c640a3849c429248ecf845476007955faf3
# Parent  e467998dcc64f0437a499bc8f77e10efbe3374b4
foo

diff -r e467998dcc64 -r 64483c640a38 main.cc
--- a/main.cc	Sat Jan 24 16:36:34 2015 +0200
+++ b/main.cc	Sat Jan 24 17:49:35 2015 +0200
@@ -9,6 +9,7 @@
 bool init();
 void display();
 void draw_grid();
+void draw_frustum();
 void draw_label(const Vector2 &pos, const char *fmt, ...);
 void reshape(int x, int y);
 void keyb(unsigned char key, int x, int y);
@@ -16,6 +17,8 @@
 void mouse(int bn, int st, int x, int y);
 void motion(int x, int y);
 Vector2 screen_to_world(int x, int y);
+Vector2 project(const Vector2 &v);
+Vector2 unproject(const Vector2 &v);
 
 int win_xsz, win_ysz;
 float aspect;
@@ -24,9 +27,12 @@
 Vector2 cur_point;
 bool cur_point_valid;
 
+float proj_near = 0.5, proj_far = 50.0;
+float proj_vfov = 50.0;
+
 bool keystate[256];
 dtx_font *font;
-float pan[2], zoom = 1.0;
+float pan[2] = {0, 0.85}, zoom = 0.4;
 
 int main(int argc, char **argv)
 {
@@ -58,7 +64,7 @@
 	}
 
 	glEnable(GL_MULTISAMPLE);
-	proj.set_perspective(DEG_TO_RAD(60), 1, 0.5, 500.0);
+	proj.set_perspective(DEG_TO_RAD(proj_vfov), 1, 1.0, 50.0);
 	return true;
 }
 
@@ -73,15 +79,34 @@
 
 	draw_grid();
 
+	draw_frustum();
+
 	if(cur_point_valid) {
+		Vector2 ppt = project(cur_point);
+
 		glPointSize(7.0);
 		glBegin(GL_POINTS);
 		glColor3f(0.2, 1, 0.2);
 		glVertex2f(cur_point.x, cur_point.y);
+		glColor3f(0.7, 0.2, 0.2);
+		glVertex2f(ppt.x, ppt.y);
 		glEnd();
 
+		glEnable(GL_LINE_STIPPLE);
+		glLineStipple(4, 0xe0e0);
+
+		glBegin(GL_LINES);
+		glColor3f(0.2, 0.5, 0.2);
+		glVertex2f(cur_point.x, cur_point.y);
+		glColor3f(0.5, 0.2, 0.2);
+		glVertex2f(ppt.x, ppt.y);
+		glEnd();
+		glDisable(GL_LINE_STIPPLE);
+
 		glColor3f(0.15, 0.5, 0.15);
 		draw_label(cur_point, "(%.2f, %.2f)", cur_point.x, cur_point.y);
+		glColor3f(0.4, 0.1, 0.1);
+		draw_label(ppt, "(%.2f, %.2f)", ppt.x, ppt.y);
 	}
 
 	glutSwapBuffers();
@@ -92,20 +117,20 @@
 
 void draw_grid()
 {
-	float ymin = -1;
-	float ymax = 1;
-	float xmin = -1;
-	float xmax = 1;
-	float ticksz = 0.015;
+	float ymin = -10;
+	float ymax = 10;
+	float xmin = -10;
+	float xmax = 10;
+	float ticksz = 0.015 / zoom;
 
 	glBegin(GL_LINES);
 	glColor3f(1, 1, 1);
-	LINE(0, -1, 0, 1);
-	LINE(-1, 0, 1, 0);
+	LINE(0, -10, 0, 10);
+	LINE(-10, 0, 10, 0);
 
 	for(int i=1; i<11; i++) {
 		for(int j=0; j<2; j++) {
-			float x = (float)i / 10.0 * (j ? -1.0 : 1.0);
+			float x = 10.0 * (float)i / 10.0 * (j ? -1.0 : 1.0);
 
 			glColor3f(0.15, 0.15, 0.15);
 			LINE(x, ymin, x, ymax);
@@ -119,6 +144,26 @@
 	glEnd();
 }
 
+void draw_frustum()
+{
+	Vector2 v0, v1;
+
+	glBegin(GL_LINES);
+	glColor3f(0.2, 0.4, 0.8);
+
+	v0 = unproject(Vector2(1, 0));
+	v1 = unproject(Vector2(1, 1));
+	LINE(v0.x, v0.y, v1.x, v1.y);
+
+	v0 = unproject(Vector2(-1, 0));
+	v1 = unproject(Vector2(-1, 1));
+	LINE(v0.x, v0.y, v1.x, v1.y);
+
+	LINE(-0.5, proj_near, 0.5, proj_near);
+
+	glEnd();
+}
+
 void draw_label(const Vector2 &pos, const char *fmt, ...)
 {
 	static char buf[512];
@@ -209,11 +254,28 @@
 
 Vector2 screen_to_world(int px, int py)
 {
-	float sx = 2.0 * aspect * (1.0 / zoom) / (float)win_xsz;
-	float sy = 2.0 * (1.0 / zoom) / (float)win_ysz;
+	/* canonical [-1, 1] system */
+	float x = aspect * ((float)px * 2.0 / (float)win_xsz - 1.0);
+	float y = (float)(win_ysz - py) * 2.0 / (float)win_ysz - 1.0;
 
-	float x = (float)px * sx - (aspect + pan[0]) / zoom;
-	float y = (float)(win_ysz - py) * sy - (1.0 + pan[1]) / zoom;
+	/* account for pan & zoom */
+	x = (x + pan[0]) / zoom;
+	y = (y + pan[1]) / zoom;
 
 	return Vector2(x, y);
 }
+
+Vector2 project(const Vector2 &v)
+{
+	Vector4 ppt = Vector4(v.x, 0, -v.y, 1).transformed(proj);
+	return Vector2(ppt.x / ppt.w, ppt.z / ppt.w);
+}
+
+Vector2 unproject(const Vector2 &v)
+{
+	Vector4 v4 = Vector4(v.x, 0.0, v.y, 1.0);
+	Matrix4x4 inv_proj = proj.inverse();
+
+	Vector4 res4 = v4.transformed(inv_proj);
+	return Vector2(res4.x / res4.w, -res4.z / res4.w);
+}