diff options
| -rw-r--r-- | assets/ball_f.glsl | 2 | ||||
| -rw-r--r-- | sim.c | 103 | ||||
| -rw-r--r-- | sim.h | 8 |
3 files changed, 100 insertions, 13 deletions
diff --git a/assets/ball_f.glsl b/assets/ball_f.glsl index e3dfdb3..779a0ec 100644 --- a/assets/ball_f.glsl +++ b/assets/ball_f.glsl @@ -5,7 +5,7 @@ uniform float radius; void main() { float dist_squared = dot(pos - center, pos - center); - float threshold = 0.9 * radius; // radius border starts at + float threshold = 0.8 * radius; // radius border starts at float thickness = radius - threshold; if (dist_squared > threshold * threshold && dist_squared < radius * radius) { @@ -196,8 +196,9 @@ static void platforms_render(State *state, Platform *platforms, u32 nplatforms) // render the ball static void ball_render(State *state) { GL *gl = &state->gl; - float ball_x = 0.5f, ball_y = 0.8f; - float ball_r = 0.02f; + 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); @@ -216,6 +217,62 @@ static void ball_render(State *state) { 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 @@ -252,7 +309,7 @@ void sim_frame(Frame *frame) { glClearColor(0, 0, 0, 1); glClear(GL_COLOR_BUFFER_BIT); - if (keys_pressed[KEY_F5]) { + if (state->magic_number != MAGIC_NUMBER || keys_pressed[KEY_F5]) { memset(state, 0, sizeof *state); } @@ -300,15 +357,22 @@ void sim_frame(Frame *frame) { shaders_load(state); - 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(0.2f, 0.5f); - p->angle = PIf * 0.6f; - p->size = 0.1f; + { // 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; @@ -325,6 +389,21 @@ void sim_frame(Frame *frame) { 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); @@ -110,6 +110,12 @@ typedef struct { } Platform; typedef struct { + v2 pos; // position + v2 vel; // velocity + float radius; +} Ball; + +typedef struct { bool initialized; i32 win_width, win_height; // width,height of window @@ -122,6 +128,8 @@ typedef struct { ShaderPlatform shader_platform; ShaderBall shader_ball; + Ball ball; + u32 nplatforms; Platform platforms[1000]; |