/apps/demos/scenery: some friction
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veclavtalica
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5abd1ced1c
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@ -53,14 +53,16 @@ static float heightmap[TERRAIN_DISTANCE][TERRAIN_DISTANCE];
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/* else if length(v(o) + (F(o)/m)*t) <= (f(k)*x(n)*t), v(o) = 0 */
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/* else, F = -unit(v(o)*f(k)*x(n)) */
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#define VEHICLE_MASS 10.0f
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#define VEHICLE_MASS 200.0f
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#define VEHICLE_LENGTH 3.0f
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#define VEHICLE_WIDTH 1.7f
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#define VEHICLE_HEIGHT 1.3f
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/* spring constant */
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#define VEHICLE_SPRING_K 20.0f
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#define VEHICLE_SPRING_K 400.0f
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/* damping constant */
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#define VEHICLE_SPRING_C 50.0f
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#define VEHICLE_SPRING_C 20.0f
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#define VEHICLE_FRICTION_S 1000000.0f
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#define VEHICLE_FRICTION_K 1000000.0f
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/* initial, ideal corner positions */
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static const Vec3 vbpi[8] = {
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@ -110,11 +112,11 @@ static void draw_vehicle(SceneIngame *scn) {
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static void process_vehicle(SceneIngame *scn) {
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/* apply gravity */
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Vec3 Facc[8] = {0};
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Vec3 const Fg = { .y = -VEHICLE_MASS * G_CONST };
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for (size_t i = 0; i < 8; ++i) {
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Vec3 const vd = vec3_scale(Fg, (1.0f / VEHICLE_MASS) * ctx.frame_duration);
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vbv[i] = vec3_add(vbv[i], vd);
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}
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for (size_t i = 0; i < 8; ++i)
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Facc[i] = vec3_add(Facc[i], Fg);
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/* apply springs */
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for (size_t i = 0; i < 24; ++i) {
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@ -129,30 +131,54 @@ static void process_vehicle(SceneIngame *scn) {
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float const x = vec3_length(pd) - lar;
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float const v = vec3_dot(vec3_sub(v1, v0), pn);
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Vec3 const Fs = vec3_scale(pn, -VEHICLE_SPRING_K * x - VEHICLE_SPRING_C * v);
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Vec3 const vd = vec3_scale(Fs, (1.0f / VEHICLE_MASS) * ctx.frame_duration);
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vbv[vbs[i][0]] = vec3_sub(vbv[vbs[i][0]], vd);
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vbv[vbs[i][1]] = vec3_add(vbv[vbs[i][1]], vd);
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Facc[vbs[i][0]] = vec3_sub(Facc[vbs[i][0]], Fs);
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Facc[vbs[i][1]] = vec3_add(Facc[vbs[i][1]], Fs);
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}
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/* spring out points that are underground */
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/* spring and friction against the ground */
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for (size_t i = 0; i < 8; ++i) {
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Vec3 const p = vbp[i];
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Vec3 const v = vbv[i];
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float const h = height_at(scn, (Vec2){ p.x, p.z });
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if (h > p.y) {
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/* displacement force */
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Vec3 const n = normal_at(scn, (Vec2){ p.x, p.z });
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float const xn = (h - p.y) * n.y;
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float const vn = vec3_dot(v, n);
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Vec3 const Fd = vec3_scale(n, -VEHICLE_SPRING_K * xn - VEHICLE_SPRING_C * vn);
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vbv[i] = vec3_add(vbv[i], vec3_scale(Fd, -(1.0f / VEHICLE_MASS) * ctx.frame_duration));
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Facc[i] = vec3_sub(Facc[i], Fd);
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/* friction force, perpendicular to displacement */
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/* portions aligned to surface normal */
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Vec3 const vov = vec3_sub(v, vec3_scale(n, vn));
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float const vo = vec3_length(vov);
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Vec3 const Fov = vec3_sub(Facc[i], vec3_scale(n, vec3_dot(Facc[i], n)));
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float const Fo = vec3_length(Fov);
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float const fkxn = VEHICLE_FRICTION_K * xn;
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if (fabsf(0.0f - vo) <= 0.0001f) {
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/* cannot overcome static friction, zero force along the surface */
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if (Fo <= VEHICLE_FRICTION_S * xn) {
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Facc[i] = vec3_sub(Facc[i], Fov);
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}
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/* apply kinematic friction */
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else {
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Facc[i] = vec3_sub(Facc[i], vec3_scale(vec3_norm(Fov), fkxn));
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}
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/* velocity with gain along the surface will not overcome */
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} else if (vo + (Fo / VEHICLE_MASS) * ctx.frame_duration <= fkxn * ctx.frame_duration) {
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vbv[i] = vec3_sub(vbv[i], vov);
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} else {
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Facc[i] = vec3_sub(Facc[i], vec3_scale(vec3_norm(vov), fkxn));
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}
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}
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}
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/* apply velocity */
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/* integrate forces and velocity */
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for (size_t i = 0; i < 8; ++i) {
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Vec3 const vd = vec3_scale(Facc[i], (1.0f / VEHICLE_MASS) * ctx.frame_duration);
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vbv[i] = vec3_add(vbv[i], vd);
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vbp[i] = vec3_add(vbp[i], vbv[i]);
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vbv[i] = vec3_scale(vbv[i], 0.99f); /* friction... */
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vbv[i] = vec3_scale(vbv[i], 0.99f);
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}
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}
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@ -188,8 +214,8 @@ static void process_fly_mode(State *state) {
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/* TODO: could be baked in map format */
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static Vec3 normal_at(SceneIngame *scn, Vec2 position) {
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int const x = (int)(HALF_TERRAIN_DISTANCE + (position.x - scn->pos.x));
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int const y = (int)(HALF_TERRAIN_DISTANCE + (position.y - scn->pos.z));
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int const x = (int)(roundf(HALF_TERRAIN_DISTANCE + (position.x - scn->pos.x)));
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int const y = (int)(roundf(HALF_TERRAIN_DISTANCE + (position.y - scn->pos.z)));
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float const height0 = heightmap[x][y];
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float const height1 = heightmap[x + 1][y];
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@ -203,31 +229,22 @@ static Vec3 normal_at(SceneIngame *scn, Vec2 position) {
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/* TODO: don't operate on triangles, instead interpolate on quads */
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static float height_at(SceneIngame *scn, Vec2 position) {
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float height0, height1, height2, weight0, weight1, weight2;
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int const x = (int)(roundf(HALF_TERRAIN_DISTANCE + (position.x - scn->pos.x)));
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int const y = (int)(roundf(HALF_TERRAIN_DISTANCE + (position.y - scn->pos.z)));
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int const x = (int)(HALF_TERRAIN_DISTANCE + (position.x - scn->pos.x));
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int const y = (int)(HALF_TERRAIN_DISTANCE + (position.y - scn->pos.z));
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height0 = heightmap[x][y];
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height1 = heightmap[x + 1][y + 1];
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float const height0 = heightmap[x][y];
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float const height1 = heightmap[x + 1][y];
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float const height2 = heightmap[x][y + 1];
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float const height3 = heightmap[x + 1][y + 1];
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Vec2 incell = { position.x - floorf(position.x), position.y - floorf(position.y) };
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/* who needs barycentric coordinates, am i right? */
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weight0 = 1 / sqrtf(powf(incell.x, 2) + powf(incell.y, 2));
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weight1 = 1 / sqrtf(powf(1 - incell.x, 2) + powf(1 - incell.y, 2));
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float const weight0 = (1 - incell.x) * (1 - incell.y);
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float const weight1 = ( incell.x) * (1 - incell.y);
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float const weight2 = (1 - incell.x) * ( incell.y);
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float const weight3 = ( incell.x) * ( incell.y);
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/* find which triangle we're directly under */
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/* for this manhattan distance is sufficient */
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if (incell.x + (1 - incell.y) < (1 - incell.x) + incell.y) {
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height2 = heightmap[x][y + 1];
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weight2 = 1 / sqrtf(powf(incell.x, 2) + powf(1 - incell.y, 2));
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} else {
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height2 = heightmap[x + 1][y];
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weight2 = 1 / sqrtf(powf(1 - incell.x, 2) + powf(incell.y, 2));
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}
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return (height0 * weight0 + height1 * weight1 + height2 * weight2) / (weight0 + weight1 + weight2);
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return (height0 * weight0 + height1 * weight1 + height2 * weight2 + height3 * weight3) / (weight0 + weight1 + weight2 + weight3);
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}
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