85 lines
3.9 KiB
Plaintext
85 lines
3.9 KiB
Plaintext
PLAYING AMBIENT SOUND WHEN CAMERA IS OVER BUILDING
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==================================================
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data flow:
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C++ JS
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> list of visible entities (1)
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< list of sound requests and their weights
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list of changed sounds
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C++ code generates list of entities on screen
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rationale: done in C++ for performance and to avoid having to expose the "patch" subdivision scheme to JS.
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UPDATE: this is much thornier than expected.
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1) we only want stuff that is visible to be played. hearing things off screen would be distressing and weird
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2) don't play sound for buildings in FoW, to prevent "audio spying"
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most straightforward way is simply scan all entities; if building, check against visible frustum.
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if inside AND within 3d distance cutoff of viewer pos, add to visible_building
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optimization for later: get all patches within 3d distance cutoff; discard all not within frustum; only test
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entities within those remaining patches.
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pass that to JS decideWhatToPlay
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it returns list of sounds it wants playing
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format: see AmbientSoundReq below
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C++ sound engine compares its list of currently sounds;
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fades out those no longer wanted and starts new ones immediately
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new entity properties needed:
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-----------------------------
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- ambientGroup: a soundGroup of several sounds; one is picked at random to be played (see below)
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- priority: to determine which entity should trump the others in a crowded city.
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// weight is so that we can play several ambient sounds at a time, but ones for buildings at edge of screen are quieter
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// values: 0..1; probably calculated from distance to camera
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type AmbientSoundReq = (SoundGroupString, weight)
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// (suggestion only; may be revised if too much cacophony/constant sound results)
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JS_decideWhatToPlay(in HEntity visible_ents[], out AmbientSoundReq desired_ambient_sounds[])
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{
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// * "important" means the building is at center of attention and should mostly override the other sounds.
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// this is complicated as well. the camera may have any orientation, especially in cinematic mode;
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// that means we can't just rely on casting a ray from viewer through middle screen pixel to terrain.
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// our building list already covers only the visible ones, so we can use 3d distance from viewer
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// (without worrying about including buildings behind us i.e. out of sight).
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// important := fairly small distance (covers the case where users zoom really close to a building) OR
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// building is close to center of screen (as determined via ray cast method; skip this if the camera
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// is weird, i.e. looking above the horizon, in which case the ray cast would fail).
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// note: not playing sounds when looking down vertically at the town but zoomed out very far is ok (desirable even).
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if an entity is important(*)
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desired_ambient_sounds[i++] = ent.ambientGroup
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forall ambient types (farm, dock etc.) in decreasing order of priority
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stop if >= 3 sounds in list
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if enough buildings on screen
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desired_ambient_sounds[i++] = ent.ambientGroup
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maybe add some random variation to spice things up? (i.e. also play some other building sounds;
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don't always have one building override the others)
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}
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C++ code keeps a list of all active sounds:
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type ActiveSound = (Handle, SoundGroupString)
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ActiveSound active_sound_list[]
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Handle startPlayingAmbient(soundGroup, weight)
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{
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filename = soundGroup.pickRandom()
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return snd_play(filename, globalAmbientVolume*soundGroup.volume*weight)
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}
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updateAmbientSounds(desired_ambient_sounds)
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{
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for all in desired_ambient_sounds but not active_sound_list:
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handle = startPlayingAmbient(amb.group, amb.weight)
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active_sound_list[i++] = (handle, amb.group)
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for all in active_sound_list but not desired_ambient_sounds:
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snd_fade(OUT, active.handle)
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}
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RANDOMIZED SOUNDS
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==================================================
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(needed for ambient and normal battle sounds) |