path: root/sim.c

#include "gui.h"
#ifdef _WIN32
#include <windows.h>
#include "lib/glcorearb.h"
#endif
#include <GL/gl.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <assert.h>
#include <ctype.h>

#define MATH_GL
#include "math.c"
#include "sim.h"
#include "time.c"
#include "util.c"
#include "base.c"

// compile a vertex or fragment shader
static GLuint shader_compile_from_file(GL *gl, char const *filename, GLenum shader_type) {
	FILE *fp = fopen(filename, "rb");
	if (fp) {
		char code[16384] = {0};
		char log[4096] = {0};
		char const *const_code = code;
		fread(code, 1, sizeof code, fp);
		GLuint shader = gl->CreateShader(shader_type);
		if (shader == 0) {
			logln("Couldn't create shader: %u",glGetError());
		}
		gl->ShaderSource(shader, 1, &const_code, NULL);
		gl->CompileShader(shader);
		gl->GetShaderInfoLog(shader, sizeof log - 1, NULL, log);
		if (*log) {
			logln("Error compiling shader:\n%s", log);
			gl->DeleteShader(shader);
			return 0;
		}
		return shader;
	} else {
		logln("File does not exist: %s.", filename);
		return 0;
	}
}

#if DEBUG
static struct timespec shader_get_last_modified(ShaderBase *shader) {
	// the last modified time of the shader is whichever of the vertex/fragment shaders was modified last
	return timespec_max(
		time_last_modified(shader->vertex_filename),
		time_last_modified(shader->fragment_filename)
	);
}
#endif

static GLuint shader_attrib_location(GL *gl, ShaderBase *shader, char const *attrib) {
	GLint loc = gl->GetAttribLocation(shader->program, attrib);
	if (loc == -1) {
		printf("Couldn't find vertex attribute %s.\n", attrib);
		return 0;
	}
	return (GLuint)loc;
}

static GLint shader_uniform_location(GL *gl, ShaderBase *shader, char const *uniform) {
	GLint loc = gl->GetUniformLocation(shader->program, uniform);
	if (loc == -1) {
		printf("Couldn't find uniform: %s.\n", uniform);
		return -1;
	}
	return loc;
}

// compile a full shader program
static void shader_load(GL *gl, ShaderBase *shader, char const *vertex_filename, char const *fragment_filename) {
#if DEBUG
	str_cpy(shader->vertex_filename, sizeof shader->vertex_filename, vertex_filename);
	str_cpy(shader->fragment_filename, sizeof shader->fragment_filename, fragment_filename);
	shader->last_modified = shader_get_last_modified(shader);

	if (shader->program) gl->DeleteProgram(shader->program);
#endif

	
	GLuint vertex_shader = shader_compile_from_file(gl, vertex_filename, GL_VERTEX_SHADER);
	GLuint fragment_shader = shader_compile_from_file(gl, fragment_filename, GL_FRAGMENT_SHADER);
	GLuint program = gl->CreateProgram();
	gl->AttachShader(program, vertex_shader);
	gl->AttachShader(program, fragment_shader);
	gl->LinkProgram(program);
	char log[4096] = {0};
	gl->GetProgramInfoLog(program, sizeof log - 1, NULL, log);
	if (*log) {
		logln("Error linking shader:\n%s", log);
		gl->DeleteProgram(program);
		program = 0;
	}
	gl->DeleteShader(vertex_shader);
	gl->DeleteShader(fragment_shader);
	shader->program = program;

	GLenum err = glGetError();
	if (err) {
		logln("Error loading shader %s/%s: %u.", vertex_filename, fragment_filename, err);
	} else {
		logln("Loaded shader %s/%s as %u.", vertex_filename, fragment_filename, program);
	}
}

static void shader_start_using(GL *gl, ShaderBase *shader) {
	gl->UseProgram(shader->program);
}

static void shader_stop_using(GL *gl) {
	gl->UseProgram(0);
}

#if DEBUG
static bool shader_needs_reloading(ShaderBase *shader) {
	return !timespec_eq(shader->last_modified, shader_get_last_modified(shader));
}
#endif

static void shader_platform_load(GL *gl, ShaderPlatform *shader) {
	ShaderBase *base = &shader->base;
	shader_load(gl, base, "assets/platform_v.glsl", "assets/platform_f.glsl");
	shader->vertex_p1 = shader_attrib_location(gl, base, "vertex_p1");
	shader->vertex_p2 = shader_attrib_location(gl, base, "vertex_p2");
	shader->uniform_thickness = shader_uniform_location(gl, base, "thickness");
	shader->uniform_transform = shader_uniform_location(gl, base, "transform");
}

static void shader_ball_load(GL *gl, ShaderBall *shader) {
	ShaderBase *base = &shader->base;
	shader_load(gl, base, "assets/ball_v.glsl", "assets/ball_f.glsl");
	shader->uniform_transform = shader_uniform_location(gl, base, "transform");
	shader->uniform_center = shader_uniform_location(gl, base, "center");
	shader->uniform_radius = shader_uniform_location(gl, base, "radius");
}

static void shaders_load(State *state) {
	GL *gl = &state->gl;
	shader_platform_load(gl, &state->shader_platform);
	shader_ball_load(gl, &state->shader_ball);
}

#if DEBUG
static void shaders_reload_if_necessary(State *state) {
	GL *gl = &state->gl;
	if (shader_needs_reloading(&state->shader_platform.base))
		shader_platform_load(gl, &state->shader_platform);
	if (shader_needs_reloading(&state->shader_ball.base))
		shader_ball_load(gl, &state->shader_ball);
}
#endif

// render the given platforms
static void platforms_render(State *state, Platform *platforms, u32 nplatforms) {
	GL *gl = &state->gl;
	ShaderPlatform *shader = &state->shader_platform;
	float thickness = 0.005f;

	shader_start_using(gl, &shader->base);
	
	gl->Uniform1f(shader->uniform_thickness, thickness);
	gl->UniformMatrix4fv(shader->uniform_transform, 1, GL_FALSE, state->transform.e);

	glBegin(GL_QUADS);
	glColor3f(1,0,1);
	for (Platform *platform = platforms, *end = platform + nplatforms; platform != end; ++platform) {
		// calculate endpoints of platform
		maybe_unused float radius = platform->size * 0.5f;
		v2 endpoint1 = v2_add(platform->center, v2_polar(radius, platform->angle));
		v2 endpoint2 = v2_sub(platform->center, v2_polar(radius, platform->angle));

	#if 1
		v2 r = v2_polar(thickness, platform->angle - HALF_PIf);
		gl->VertexAttrib2f(shader->vertex_p1, endpoint1.x, endpoint1.y);
		gl->VertexAttrib2f(shader->vertex_p2, endpoint2.x, endpoint2.y);
		v2_gl_vertex(v2_sub(endpoint1, r));
		v2_gl_vertex(v2_sub(endpoint2, r));
		v2_gl_vertex(v2_add(endpoint2, r));
		v2_gl_vertex(v2_add(endpoint1, r));
	#else
		v2_gl_vertex(endpoint1);
		v2_gl_vertex(endpoint2);
	#endif
	}
	glEnd();
	shader_stop_using(gl);
}

// render the ball
static void ball_render(State *state) {
	GL *gl = &state->gl;
	Ball *ball = &state->ball;
	float ball_x = ball->pos.x, ball_y = ball->pos.y;
	float ball_r = ball->radius;
	ShaderBall *shader = &state->shader_ball;
	
	shader_start_using(gl, &shader->base);
	
	gl->UniformMatrix4fv(shader->uniform_transform, 1, GL_FALSE, state->transform.e);
	gl->Uniform2f(shader->uniform_center, ball_x, ball_y);
	gl->Uniform1f(shader->uniform_radius, ball_r);

	glBegin(GL_QUADS);
	glColor3f(1,1,1);
	glVertex2f(ball_x-ball_r, ball_y-ball_r);
	glVertex2f(ball_x-ball_r, ball_y+ball_r);
	glVertex2f(ball_x+ball_r, ball_y+ball_r);
	glVertex2f(ball_x+ball_r, ball_y-ball_r);
	glEnd();
	shader_stop_using(gl);
}

// calculate new position/velocity of ball
static void ball_update(State *state, float dt) {
	Ball *ball = &state->ball;
	float ball_r_squared = ball->radius * ball->radius;
	float gravity = 0.001f;
	v2 *vel = &ball->vel;
	v2 acceleration = V2(0, -gravity);
	// apply velocity to position
	v2 ball_pos = v2_add(ball->pos, v2_scale(*vel, dt));
	// correct position according to acceleration (p' = p + v⋅t + 1/2⋅a⋅t²)
	ball_pos = v2_add(ball_pos, v2_scale(acceleration, 0.5f * dt * dt));
	// apply acceleration to velocity
	*vel = v2_add(*vel, acceleration);
	for (Platform *platform = state->platforms, *end = platform + state->nplatforms;
		platform != end; ++platform) {
		v2 platform_center = platform->center;
		float platform_size = platform->size;
		float platform_angle = platform->angle;
		v2 platform_length = v2_polar(platform_size, platform_angle);
		platform_center = v2_sub(platform_center, ball_pos); // now the center of the ball is (0, 0)
		v2 platform_pos = v2_sub(platform_center, v2_scale(platform_length, 0.5f));

		// do some math to figure out if the ball & platform intersect
		float dot = v2_dot(platform_length, platform_pos);
		float len_squared = v2_dot(platform_length, platform_length);
		float pos_squared = v2_dot(platform_pos, platform_pos);
		float discriminant = dot * dot - len_squared * (pos_squared - ball_r_squared);
		if (discriminant < 0) {
			// full line (not segment) defined by platform doesn't even intersect ball, let alone the platform proper
		} else {
			float one_over_len_squared = 1.0f / len_squared;
			float d1 = (-dot - sqrtf(discriminant)) * one_over_len_squared;
			float d2 = (-dot + sqrtf(discriminant)) * one_over_len_squared;
			// points platform_pos + d1 * platform_len and
			//        platform_pos + d2 * platform_len
			// are where the platform intersects the circle.
			// if either is between 0 and 1, then the intersection actually happens on the platform
			if ((d1 >= 0 && d1 <= 1) || (d2 >= 0 && d2 <= 1)) {
				// platform intersects ball
				float d = (d1 >= 0 && d1 <= 1) ? d1 : d2;
				v2 collide_pos = v2_add(platform_pos, v2_scale(platform_length, d));

				// calculate new velocity after collision
				float vel_angle = -atan2f(vel->y, vel->x);
				float vel_angle_relative_to_platform = vel_angle - platform->angle;
				float new_angle = vel_angle + (PIf - 2 * vel_angle_relative_to_platform);
				*vel = v2_polar(v2_len(*vel), new_angle);
				ball_pos = v2_add(ball->pos, v2_scale(*vel, dt));
				break;
			}
		}

	}
	ball->pos = ball_pos;
}

#ifdef _WIN32
__declspec(dllexport)
#endif
#ifdef __cplusplus
extern "C"
#endif
void sim_frame(Frame *frame) {
	if (frame->memory_size < sizeof(State)) {
		printf("Not enough memory (got %lu, require %lu).\n", (ulong)frame->memory_size, (ulong)sizeof(State));
		frame->close = true;
		return;
	}
	State *state = (State *)frame->memory;
	i32 width = frame->width, height = frame->height;
	Input *input = &frame->input;
	GL *gl = &state->gl;
	maybe_unused u8 *keys_pressed = input->keys_pressed;
	maybe_unused bool *keys_down = input->keys_down;

	state->win_width  = width;
	state->win_height = height;
	state->gl_width = (float)width / (float)height;
	state->dt = (float)frame->dt;
	
	state->transform = m4_ortho(0, state->gl_width, 0, 1, -1, +1);

	// set up GL
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glViewport(0, 0, width, height);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glOrtho(0, state->gl_width, 0, 1, -1, +1);
	glClearColor(0, 0, 0, 1);
	glClear(GL_COLOR_BUFFER_BIT);
	
	if (state->magic_number != MAGIC_NUMBER || keys_pressed[KEY_F5]) {
		memset(state, 0, sizeof *state);
	}


	if (!state->initialized) {
		logln("Initializing...");
		strcpy(frame->title, "physics");

		void (*(*get_gl_proc)(char const *))(void) = frame->get_gl_proc;

		// get GL functions
	#define required_gl_proc(name) if (!(gl->name = (GL ## name)get_gl_proc("gl" #name))) { printf("Couldn't get GL proc: %s.\n", #name); exit(-1); }
	#define optional_gl_proc(name) gl->name = (GL ## name)get_gl_proc("gl" #name)
		required_gl_proc(AttachShader);
		required_gl_proc(CompileShader);
		required_gl_proc(CreateProgram);
		required_gl_proc(CreateShader);
		required_gl_proc(DeleteProgram);
		required_gl_proc(DeleteShader);
		required_gl_proc(GetAttribLocation);
		required_gl_proc(GetProgramInfoLog);
		required_gl_proc(GetProgramiv);
		required_gl_proc(GetShaderInfoLog);
		required_gl_proc(GetShaderiv);
		required_gl_proc(GetUniformLocation);
		required_gl_proc(LinkProgram);
		required_gl_proc(ShaderSource);
		required_gl_proc(Uniform1f);
		required_gl_proc(Uniform2f);
		required_gl_proc(Uniform3f);
		required_gl_proc(Uniform4f);
		required_gl_proc(Uniform1i);
		required_gl_proc(Uniform2i);
		required_gl_proc(Uniform3i);
		required_gl_proc(Uniform4i);
		required_gl_proc(UniformMatrix4fv);
		required_gl_proc(UseProgram);
		required_gl_proc(VertexAttrib1f);
		required_gl_proc(VertexAttrib2f);
		required_gl_proc(VertexAttrib3f);
		required_gl_proc(VertexAttrib4f);
	#undef optional_gl_proc
	#undef required_gl_proc

		shaders_load(state);
		

		{ // initialize platforms
			state->nplatforms = 2;
			Platform *p = &state->platforms[0];
			p->center = V2(0.5f, 0.5f);
			p->angle  = PIf * 0.3f;
			p->size   = 0.2f;
			++p;
			p->center = V2(0.4f, 0.5f);
			p->angle  = PIf * 0.7f;
			p->size   = 0.2f;
		}

		Ball *ball = &state->ball;
		ball->radius = 0.002f;
		ball->pos = V2(0.5f, 0.8f);
		ball->vel = V2(0, 0);

		
		state->initialized = true;
	#if DEBUG
		state->magic_number = MAGIC_NUMBER;
	#endif
	}
	if (input->keys_pressed[KEY_ESCAPE]) {
		frame->close = true;
		return;
	}

#if DEBUG
	shaders_reload_if_necessary(state);
#endif

	// simulate physics
	{
		float dt = state->dt;
		float physics_step = 0.01f; // maximum dt for each physics step
		if (dt > 100)
			dt = 100; // make sure that dt -= physics_step actually does something (if dt is very large, it might not)
		// do a number of fixed dt steps
		while (dt > physics_step) {
			ball_update(state, physics_step);
			dt -= physics_step;
		}
		// update for remaining time
		ball_update(state, dt);
	}

	platforms_render(state, state->platforms, state->nplatforms);
	ball_render(state);

	#if DEBUG
	GLuint error = glGetError();
	if (error) {
		printf("!!! GL ERROR: %u\n", error);
	}
	#endif
}