OpenGL : Blending & feedback effect

I’m struggling on a simple project, as an example/sandbox, I’m rendering a small oscillating rectangle on my output. I’m not using glclearcolor() but instead, on every frame I draw a black rectangle before anything else, blending with glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

My goal is to see as I play with the alpha of this black rectangle feedback of previous frames, slowly fading, some kind of trail, and it’s more or less working.

My main problem though, the trail never really disappears, and the longer I try to get the trail, the worse it gets. Also, I have to quite crank the alpha before seeing any trail, I don’t really understand why.

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Is a target pushed into a wall by a spell effect subject to collision damage?

Some spells can push the target X feet away (like thunderwave, which pushes 10 feet away on a failed save). I was wondering what happens if the target, while being pushed, encounters a wall or other rigid object. Does it take (bludgeoning) damage? To me it seems logical that it would: it is like falling, sudden force applied to a creature due to encountering resistance from an object.

I couldn’t find any rules about this in the Player’s Handbook nor online.

When does a Taunt action take effect during starship combat?

According to Starfinder’s starship combat rules on the Captain’s Taunt action:

You can use the communications system to broadcast a taunting message to the enemy vessel. You select an enemy vessel and a phase of combat (engineering, helm, or gunnery), and then attempt a Bluff or Intimidate check (DC = 15 + 1-1/2 × the enemy starship’s tier). If you are successful, each enemy character acting during the selected phase takes a –2 penalty to all checks for 1d4 rounds; the penalty increases to –4 if the enemy’s check is made as part of a push action. Once used against an enemy starship, regardless of the outcome, taunt can’t be used against that starship again during the same combat.

My question is when do these penalties take effect?

Example of why this is unclear: In round 1’s helm phase, on behalf of an NPC crew, the GM rolls for the piloting check, a piloting stunt, and a science officer action. Then, after these rolls have been made but during the same helm phase, the player Captaining the PC ship successfully Taunts the NPC ship and rolls a 3 for rounds of effect.

Does the -2 penalty apply retroactively to the GM’s die rolls in round 1 and then continue for rounds 2 and 3? Does the penalty last until round 3, but the NPC crew escaped the effects for round 1 because the GM rolled before the player? Or does the -2 penalty kick in at the beginning of round 2 and last until round 4, guaranteeing the NPCs suffer three rounds of effects even though they avoided the penalty in round 1?

Would the Gust spell be able to move someone under the effect of the Levitate spell?

I am playing an air genasi storm sorcerer. Air genasi have the Mingle with the Wind racial trait, which lets them cast the levitate spell once per long rest (with no material components).

The description of the levitate spell says:

One creature or object of your choice that you can see within range rises vertically, up to 20 feet, and remains suspended there for the duration. The spell can levitate a target that weighs up to 500 pounds. An unwilling creature that succeeds on a Constitution saving throw is unaffected.

The target can move only by pushing or pulling against a fixed object or surface within reach (such as a wall or a ceiling), which allows it to move as if it were climbing. You can change the target’s altitude by up to 20 feet in either direction on your turn. If you are the target, you can move up or down as part of your move. Otherwise, you can use your action to move the target, which must remain within the spell’s range.

The description of gust states:

You seize the air and compel it to create one of the following effects at a point you can see within range:

  • One Medium or smaller creature that you choose must succeed on a Strength saving throw or be pushed up to 5 feet away from you.

  • You create a small blast of air capable of moving one object that is neither held nor carried and that weighs no more than 5 pounds. The object is pushed up to 10 feet away from you. It isn’t pushed with enough force to cause damage.

  • You create a harmless sensory affect using air, such as causing leaves to rustle, wind to slam shutters shut, or your clothing to ripple in a breeze.

I wanted to use the gust cantrip to move myself 5 feet in a direction, but my GM said it wouldn’t work, as levitate only allows the target to move by physical means as the spell states, and I couldn’t cast gust to target myself anyways.

I didn’t argue at the time, but having reread the spells, I’m not sure why it wouldn’t work.

Is it possible to cast levitate on yourself, then use gust to move yourself 5 feet?

What effect does learning a spell have for a sorcerer?

I’ve read and reread Learn a Spell several times, and I just don’t understand it.

For a wizard, it makes sense – the wizard adds the spell to their spellbook. But for both of the other options, I don’t understand what effect it has.

From the feat:

If you have a spellbook, Learning a Spell lets you add the spell to your spellbook; if you prepare spells from a list, it’s added to your list; if you have a spell repertoire, you can select it when you add or swap spells.

if you prepare spells from a list

What classes does this apply to? Cleric? Surely if a character prepares spells from a list, then that character has access to the entire tradition’s spell list – what benefit does learning a spell have for a class like Cleric or Druid?

if you have a spell repertoire, you can select it when you add or swap spells.

For a class like Sorcerer, as I understand it their repertoire can only ever contain as many spells as the number of spell slots they have.

So let’s say at level 1, a draconic sorcerer uses the Learn a Spell activity to learn Fear, a spell in the Arcane tradition. They don’t have Fear in their repertoire already, and they succeed at the check. If I’m right, then can’t use that spell until they level up, or spend downtime swapping another spell in their repertoire out for that spell.

But this doesn’t make sense to me either – the way the spell repertoire feature is phrased, it makes it sound like the sorcerer would be able to swap out one of the spells in their repertoire for any spell of the same level in the Arcane tradition’s spell list (Fear included) anyway when they level up – so what was the point of learning it?

Is there a subset of tradition spells that a sorcerer knows, which is somehow distinct from the sorcerer’s repertoire?

Or is the activity purely intended to allow spontaneous casters to add uncommon-or-rarer spells to their repertoire?

If someone can explain this to me, I’d really appreciate it!

Does plant growth’s 8 hour effect stack? [duplicate]

If you cast Plant Growth for its 8-hour version to

[…] enrich the land. All plants in a half-mile radius centered on a point within range become enriched for 1 year. The plants yield twice the normal amount of food when harvested.

and then come back the next day and cast it again the same way for the third time, would the total crops harvested be doubled, and then, quadrupled, and then octupled?
The campaign I am in is measured in years, so the impact of a druid (or in this case, nature cleric) who can spend 8 hours to double a 1/2 mile radius circle of food would be super helpful, but I need to know if I can prioritize one spot to make the growth exponential, vs going and casting in a different spot every day to just have a net double.

If a spell has an instantaneous duration, but an effect that lingers, can that effect be stacked?

I’ve seen this popping up for quite a few specific spells in the past, so lets get a general clarification down.

Overlapping effects says:

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don’t combine, however. Instead, the most potent effect–such as the highest bonus–from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

The part that seems to be tripping up most askers is the "while the durations overlap" text, since some spells have a duration of Instantaneous.

One of the classic examples would be Booming Blade, which has the effect of dealing a bit of damage, and then leaving a lingering effect that deals extra damage if the target moves voluntarily on their turn. Lets say we’re a sorcerer who cast Booming Blade on an enemy, and then for good measure, we cast it again with Quickened Spell Metamagic. Then our Eldritch Knight ally decides that he really wants to be sure, and strikes with Booming Blade himself, then Action Surges to do it again. Is our poor foe subject to 4 instances of Booming Blade if it so dares to move voluntarily?

Or another example, let’s say that our Cleric has cast Ceremony, and chooses Wedding (+2AC, 7 days), then casts it again on both of the newlyweds, and chooses Dedication (+1d4 to saves, 24 hours). Does our newly married and dedicated couple gain both benefits?

So to put it plainly, since instantaneous effects have a duration of, well, Instantaneous, should the spells listed duration be taken as the effects duration in regards to stacking, or should any additional duration listed in the spell, be it 1 round or 1 year, be what is primarily considered?

If it’s the latter, are there any that specifically break this rule?