feat: simple fps game

C/fps/Makefile

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+# Minimal Makefile for the simple OpenGL FPS demo
+# Targets: build (default), run, clean
+
+CC := gcc
+CFLAGS := -O2 -Wall -Wextra -Wno-missing-field-initializers -std=c11
+LDFLAGS := -lglut -lGLU -lGL -lm
+
+SRC := main.c
+BIN := fps_demo
+
+all: $(BIN)
+
+$(BIN): $(SRC)
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+run: $(BIN)
+	./$(BIN)
+
+clean:
+	rm -f $(BIN)
+
+.PHONY: all run clean

C/fps/README.md

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+# Simple OpenGL FPS (C + FreeGLUT)
+
+A tiny first-person demo using legacy OpenGL (compat) and FreeGLUT:
+- Move with WASD, hold Tab or Q to sprint
+- Aim with mouse (captured by default). Press M to toggle capture
+- Shoot with Left Mouse or Space. Hit the red cube to score; it respawns
+- Press Esc to quit
+
+## Build
+
+Requires development packages for OpenGL, GLU, and FreeGLUT.
+On Debian/Ubuntu:
+
+```sh
+sudo apt-get update
+sudo apt-get install -y build-essential freeglut3-dev
+```
+
+Then build and run:
+
+```sh
+make -C C/fps
+make -C C/fps run
+```
+
+If your distro uses different package names, install the equivalents of:
+- libgl1, libglu1, freeglut (dev headers)
+
+## Notes
+- This uses old-school fixed-function OpenGL for simplicity and broad compatibility.
+- Mouse is confined via glutWarpPointer; press M if you need to release it.

C/fps/main.c

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+// Simple FPS demo using FreeGLUT + legacy OpenGL (compat profile)
+// - Move: WASD, Shift to sprint, Space to shoot, Esc to quit
+// - Look: mouse
+// - Target: red cube; shoot to score and respawn target
+
+#include <GL/glut.h>
+#include <GL/glu.h>
+#include <math.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+// -------- Math helpers --------
+typedef struct { float x, y, z; } vec3;
+
+static inline vec3 v3(float x, float y, float z) { vec3 v = {x,y,z}; return v; }
+static inline vec3 v3_add(vec3 a, vec3 b) { return v3(a.x+b.x, a.y+b.y, a.z+b.z); }
+static inline vec3 v3_sub(vec3 a, vec3 b) { return v3(a.x-b.x, a.y-b.y, a.z-b.z); }
+static inline vec3 v3_scale(vec3 a, float s) { return v3(a.x*s, a.y*s, a.z*s); }
+static inline float v3_dot(vec3 a, vec3 b) { return a.x*b.x + a.y*b.y + a.z*b.z; }
+static inline vec3 v3_cross(vec3 a, vec3 b) {
+	return v3(a.y*b.z - a.z*b.y, a.z*b.x - a.x*b.z, a.x*b.y - a.y*b.x);
+}
+static inline float v3_len(vec3 a) { return sqrtf(v3_dot(a,a)); }
+static inline vec3 v3_norm(vec3 a) {
+	float l = v3_len(a);
+	return l > 1e-6f ? v3_scale(a, 1.0f/l) : v3(0,0,0);
+}
+
+// -------- Global state --------
+static int g_win_w = 1280, g_win_h = 720;
+static bool g_keys[256] = {0};
+static bool g_captured_mouse = true;
+static int g_last_mouse_x = -1, g_last_mouse_y = -1;
+static bool g_ignore_next_passive = false; // avoid warp feedback loops
+
+static vec3 g_cam_pos = {0.0f, 1.6f, 5.0f};
+static float g_yaw_deg = -90.0f; // facing -Z initially
+static float g_pitch_deg = 0.0f;
+
+static float g_move_speed = 4.0f; // m/s
+static float g_sprint_mul = 1.8f;
+static float g_mouse_sens = 0.12f; // deg per pixel
+
+typedef struct { vec3 pos; float radius; } Target;
+static Target g_target;
+static int g_score = 0;
+
+// Bullet visualization
+static float g_bullet_t = 0.0f; // seconds left to show bullet line
+static vec3 g_bullet_origin, g_bullet_dir;
+
+// Timing
+static int g_prev_ms = 0;
+
+// -------- Utility --------
+static float clampf(float v, float lo, float hi) { return v < lo ? lo : (v > hi ? hi : v); }
+static float deg2rad(float d) { return d * (float)M_PI / 180.0f; }
+
+static vec3 cam_front()
+{
+	float yaw = deg2rad(g_yaw_deg);
+	float pitch = deg2rad(g_pitch_deg);
+	vec3 f = { cosf(pitch)*cosf(yaw), sinf(pitch), cosf(pitch)*sinf(yaw) };
+	return v3_norm(f);
+}
+
+static vec3 cam_right()
+{
+	return v3_norm(v3_cross(cam_front(), v3(0,1,0)));
+}
+
+static void respawn_target()
+{
+	float x = ((rand()/(float)RAND_MAX) * 24.0f) - 12.0f; // [-12,12]
+	float z = ((rand()/(float)RAND_MAX) * 24.0f) - 12.0f; // [-12,12]
+	g_target.pos = v3(x, 0.5f, z);
+	g_target.radius = 0.6f; // fits a 1.0 cube roughly
+}
+
+// Ray-sphere intersection: returns t >= 0 for first hit, or -1 if miss
+static float ray_sphere(vec3 ro, vec3 rd, vec3 c, float r)
+{
+	vec3 oc = v3_sub(ro, c);
+	float b = v3_dot(oc, rd);
+	float cterm = v3_dot(oc, oc) - r*r;
+	float disc = b*b - cterm;
+	if (disc < 0.0f) return -1.0f;
+	float t = -b - sqrtf(disc);
+	return t >= 0.0f ? t : -1.0f;
+}
+
+static void shoot()
+{
+	vec3 dir = cam_front();
+	float t = ray_sphere(g_cam_pos, dir, g_target.pos, g_target.radius);
+	g_bullet_origin = g_cam_pos;
+	g_bullet_dir = dir;
+	g_bullet_t = 0.08f; // show for ~80ms
+
+	if (t >= 0.0f && t < 100.0f) {
+		g_score++;
+		char title[128];
+		snprintf(title, sizeof(title), "FPS Demo | Score: %d", g_score);
+		glutSetWindowTitle(title);
+		respawn_target();
+	}
+}
+
+// -------- Rendering --------
+static void draw_grid(float half, float step)
+{
+	glColor3f(0.2f, 0.25f, 0.3f);
+	glBegin(GL_LINES);
+	for (float x = -half; x <= half + 1e-4f; x += step) {
+		glVertex3f(x, 0.0f, -half); glVertex3f(x, 0.0f, half);
+	}
+	for (float z = -half; z <= half + 1e-4f; z += step) {
+		glVertex3f(-half, 0.0f, z); glVertex3f(half, 0.0f, z);
+	}
+	glEnd();
+}
+
+static void draw_cube()
+{
+	// Simple colored cube (size 1)
+	const float s = 0.5f;
+	glBegin(GL_QUADS);
+	// +X
+	glColor3f(1,0,0); glVertex3f( s,-s,-s); glVertex3f( s,-s, s); glVertex3f( s, s, s); glVertex3f( s, s,-s);
+	// -X
+	glColor3f(0.8f,0,0); glVertex3f(-s,-s,-s); glVertex3f(-s, s,-s); glVertex3f(-s, s, s); glVertex3f(-s,-s, s);
+	// +Y
+	glColor3f(0.9f,0.1f,0.1f); glVertex3f(-s, s,-s); glVertex3f( s, s,-s); glVertex3f( s, s, s); glVertex3f(-s, s, s);
+	// -Y
+	glColor3f(0.6f,0.05f,0.05f); glVertex3f(-s,-s,-s); glVertex3f(-s,-s, s); glVertex3f( s,-s, s); glVertex3f( s,-s,-s);
+	// +Z
+	glColor3f(1,0.2f,0.2f); glVertex3f(-s,-s, s); glVertex3f(-s, s, s); glVertex3f( s, s, s); glVertex3f( s,-s, s);
+	// -Z
+	glColor3f(0.7f,0.1f,0.1f); glVertex3f(-s,-s,-s); glVertex3f( s,-s,-s); glVertex3f( s, s,-s); glVertex3f(-s, s,-s);
+	glEnd();
+}
+
+static void draw_crosshair()
+{
+	glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity();
+	gluOrtho2D(0, g_win_w, g_win_h, 0);
+	glMatrixMode(GL_MODELVIEW); glPushMatrix(); glLoadIdentity();
+
+	glDisable(GL_DEPTH_TEST);
+	glColor3f(0.95f, 0.95f, 0.95f);
+	int cx = g_win_w/2, cy = g_win_h/2;
+	int s = 8;
+	glBegin(GL_LINES);
+	glVertex2i(cx - s, cy); glVertex2i(cx + s, cy);
+	glVertex2i(cx, cy - s); glVertex2i(cx, cy + s);
+	glEnd();
+	glEnable(GL_DEPTH_TEST);
+
+	glMatrixMode(GL_MODELVIEW); glPopMatrix();
+	glMatrixMode(GL_PROJECTION); glPopMatrix();
+}
+
+static void display()
+{
+	glClearColor(0.05f, 0.06f, 0.08f, 1.0f);
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+	glMatrixMode(GL_MODELVIEW);
+	glLoadIdentity();
+
+	vec3 front = cam_front();
+	vec3 at = v3_add(g_cam_pos, front);
+	gluLookAt(g_cam_pos.x, g_cam_pos.y, g_cam_pos.z,
+			  at.x,        at.y,        at.z,
+			  0,           1,           0);
+
+	// Ground grid
+	draw_grid(40.0f, 1.0f);
+
+	// Target cube
+	glPushMatrix();
+	glTranslatef(g_target.pos.x, g_target.pos.y, g_target.pos.z);
+	draw_cube();
+	glPopMatrix();
+
+	// Bullet line
+	if (g_bullet_t > 0.0f) {
+		glColor3f(1.0f, 1.0f, 0.3f);
+		glBegin(GL_LINES);
+		vec3 p0 = g_bullet_origin;
+		vec3 p1 = v3_add(p0, v3_scale(g_bullet_dir, 100.0f));
+		glVertex3f(p0.x, p0.y, p0.z);
+		glVertex3f(p1.x, p1.y, p1.z);
+		glEnd();
+	}
+
+	// Crosshair overlay
+	draw_crosshair();
+
+	glutSwapBuffers();
+}
+
+// -------- Update/Input --------
+static void update(float dt)
+{
+	float speed = g_move_speed * ((g_keys['\t'] || g_keys['Q'] || g_keys['q']) ? g_sprint_mul : 1.0f); // Tab/Q to sprint
+	vec3 f = cam_front(); f.y = 0.0f; f = v3_norm(f);
+	vec3 r = cam_right(); r.y = 0.0f; r = v3_norm(r);
+
+	if (g_keys['W'] || g_keys['w']) g_cam_pos = v3_add(g_cam_pos, v3_scale(f, speed*dt));
+	if (g_keys['S'] || g_keys['s']) g_cam_pos = v3_sub(g_cam_pos, v3_scale(f, speed*dt));
+	if (g_keys['A'] || g_keys['a']) g_cam_pos = v3_sub(g_cam_pos, v3_scale(r, speed*dt));
+	if (g_keys['D'] || g_keys['d']) g_cam_pos = v3_add(g_cam_pos, v3_scale(r, speed*dt));
+
+	// Keep feet on ground
+	g_cam_pos.y = 1.6f;
+
+	if (g_bullet_t > 0.0f) {
+		g_bullet_t -= dt;
+		if (g_bullet_t < 0.0f) g_bullet_t = 0.0f;
+	}
+}
+
+static void idle()
+{
+	int now = glutGet(GLUT_ELAPSED_TIME);
+	if (g_prev_ms == 0) g_prev_ms = now;
+	float dt = (now - g_prev_ms) / 1000.0f;
+	g_prev_ms = now;
+
+	update(dt);
+	glutPostRedisplay();
+}
+
+static void reshape(int w, int h)
+{
+	g_win_w = w > 1 ? w : 1;
+	g_win_h = h > 1 ? h : 1;
+	glViewport(0, 0, g_win_w, g_win_h);
+	glMatrixMode(GL_PROJECTION);
+	glLoadIdentity();
+	gluPerspective(75.0, (double)g_win_w/(double)g_win_h, 0.05, 500.0);
+	glMatrixMode(GL_MODELVIEW);
+
+	if (g_captured_mouse) {
+		g_ignore_next_passive = true;
+		glutWarpPointer(g_win_w/2, g_win_h/2);
+	}
+}
+
+static void keyboard_down(unsigned char key, int x, int y)
+{
+	(void)x; (void)y;
+	g_keys[key] = true;
+	if (key == 27) { // Esc
+		exit(0);
+	} else if (key == ' ') {
+		shoot();
+	} else if (key == 'm' || key == 'M') {
+		g_captured_mouse = !g_captured_mouse;
+		glutSetCursor(g_captured_mouse ? GLUT_CURSOR_NONE : GLUT_CURSOR_LEFT_ARROW);
+		if (g_captured_mouse) {
+			g_ignore_next_passive = true;
+			glutWarpPointer(g_win_w/2, g_win_h/2);
+		}
+	}
+}
+
+static void keyboard_up(unsigned char key, int x, int y)
+{
+	(void)x; (void)y;
+	g_keys[key] = false;
+}
+
+static void mouse_button(int button, int state, int x, int y)
+{
+	(void)x; (void)y;
+	if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
+		shoot();
+	}
+}
+
+static void passive_motion(int x, int y)
+{
+	if (!g_captured_mouse) return;
+
+	if (g_ignore_next_passive) { // ignore event caused by warp
+		g_ignore_next_passive = false;
+		return;
+	}
+
+	if (g_last_mouse_x < 0) { g_last_mouse_x = x; g_last_mouse_y = y; }
+	int dx = x - g_win_w/2;
+	int dy = y - g_win_h/2;
+
+	g_yaw_deg   += dx * g_mouse_sens;
+	g_pitch_deg -= dy * g_mouse_sens;
+	g_pitch_deg = clampf(g_pitch_deg, -89.0f, 89.0f);
+
+	g_ignore_next_passive = true;
+	glutWarpPointer(g_win_w/2, g_win_h/2);
+}
+
+// -------- Init --------
+static void init_gl()
+{
+	glEnable(GL_DEPTH_TEST);
+	glEnable(GL_CULL_FACE);
+	glCullFace(GL_BACK);
+	glLineWidth(1.0f);
+}
+
+int main(int argc, char** argv)
+{
+	(void)argv;
+	srand((unsigned)time(NULL));
+	respawn_target();
+
+	glutInit(&argc, argv);
+	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
+	glutInitWindowSize(g_win_w, g_win_h);
+	glutCreateWindow("FPS Demo | Score: 0");
+
+	init_gl();
+
+	glutDisplayFunc(display);
+	glutIdleFunc(idle);
+	glutReshapeFunc(reshape);
+	glutKeyboardFunc(keyboard_down);
+	glutKeyboardUpFunc(keyboard_up);
+	glutPassiveMotionFunc(passive_motion);
+	glutMouseFunc(mouse_button);
+
+	// Start with mouse captured
+	glutSetCursor(GLUT_CURSOR_NONE);
+	g_ignore_next_passive = true;
+	glutWarpPointer(g_win_w/2, g_win_h/2);
+
+	glutMainLoop();
+	return 0;
+}