bugfix(drawable): Decouple visual render from projectile's logic position by githubawn · Pull Request #2598 · TheSuperHackers/GeneralsGameCode

githubawn · 2026-04-13T14:34:16Z

This PR fixes the visual "stutter" or "jitter" seen on drawables when playing at high framerates. While the game's internal logic updates at a fixed frequency, rendering often happens much faster, causing drawables to appear to "step" across the screen rather than move smoothly.

Implemented a system that fills in the gaps between logic steps, allowing drawables to match the user's framerate.
Created a unified way for the game's rendering system to communicate with various drawables types.

Video is of 30 logic and 60 visual, notice the projectile moving with every step:
https://github.com/user-attachments/assets/fcdefce9-723d-4d3b-aeda-d60d1fcce5de

Todo:
replicate to generals

greptile-apps · 2026-04-13T14:39:39Z

Greptile Summary

Adds sub-frame visual smoothing for Zero Hour projectiles and turret movement.

Samples consecutive logic-frame transforms and interpolates drawable position and orientation during rendering.
Interpolates turret rotation and pitch using the frame-pacing accumulator.
Exposes the logic-time accumulator through both game-specific GameEngine interfaces.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
GeneralsMD/Code/GameEngine/Source/GameClient/Drawable.cpp	Adds logic-frame transform sampling and a decoupled visual matrix used during drawable rendering.
GeneralsMD/Code/GameEngine/Include/GameClient/Drawable.h	Declares the drawable interpolation state and sub-frame transform helper.
Core/GameEngineDevice/Source/W3DDevice/GameClient/Drawable/Draw/W3DModelDraw.cpp	Adds frame-sampled interpolation for turret rotation and pitch.
Core/GameEngineDevice/Include/W3DDevice/GameClient/Module/W3DModelDraw.h	Stores previous and current turret samples for visual interpolation.
Generals/Code/GameEngine/Include/Common/GameEngine.h	Exposes the current logic-time accumulator to rendering code.
GeneralsMD/Code/GameEngine/Include/Common/GameEngine.h	Exposes the current logic-time accumulator to rendering code.

Sequence Diagram

sequenceDiagram
    participant Logic as GameLogic
    participant Engine as GameEngine
    participant Drawable as Drawable
    participant Model as W3DModelDraw
    participant Renderer as W3D Renderer
    Logic->>Drawable: Update object transform at fixed tick
    Engine->>Drawable: Provide remaining logic-time accumulator
    Drawable->>Drawable: Sample previous/current transforms
    Drawable->>Drawable: Compute sub-frame visual transform
    Model->>Model: Sample and interpolate turret angles
    Drawable->>Renderer: Render interpolated world transform
    Model->>Renderer: Render interpolated turret bones

_{Reviews (8): Last reviewed commit: "fix generals" | Re-trigger Greptile}

xezon · 2026-04-13T20:34:02Z

 {

 }
+void Drawable::setLogicVelocity(const Coord3D* velocity) 


I think this is going into the right direction and this ideally becomes applicable to ALL drawable, not just projectiles. I am not a fan of this hand holding of requiring external users to set velocities. It makes caller code more complicated.

I suggest to try implement this more generic so that any movements are interpolated between real logic frames. To do that, try to have a recycled history of 3 to 5 transforms and then extrapolate them. This could work alright even with accelleration and braking. Maybe make the history length configurable per drawable, because for objects that have no accelleration, 2 points would be enough for velocity.

…osition, rotation, and turrets

Skyaero42 · 2026-08-02T07:30:48Z


  Bool m_receivesDynamicLights;

+private:


I don't think this should be here

Skyaero42 · 2026-08-02T07:32:14Z

+			m_currLogicMtx = currentMtx;
+
+			Vector3 deltaPos = m_currLogicMtx.Get_Translation() - m_prevLogicMtx.Get_Translation();
+			if (deltaPos.Length2() > 40000.0f) // >200 units threshold for teleportation


why 40.000?
Probably should be a well documented const variable.

sqr(200.f)

In what event does teleportation occur? Is there a script action for it?

The cleaner way would be to remove the magic teleport distance and invalidate the interpolation on real teleportation events.

xezon

This is going into the right direction judging by the code. A few things can be improved.

xezon · 2026-08-02T09:03:48Z

+	m_useExtrapolation = FALSE;
+	m_visualExtrapolationMtx.Make_Identity();
+	m_prevLogicMtx.Make_Identity();
+	m_currLogicMtx.Make_Identity();


Are 2 sample points sufficient for acceleration and braking units? I would expect we need at least 3 samples to extrapolate that more accurately, because the delta of transform and rotation between N-2, N-1 and N will give a prediction scale for N to N+1 (, which may or may not be beneficial).

xezon · 2026-08-02T09:15:21Z

+		m_lastSampledLogicFrame = currentLogicFrame;
+	}
+
+	Real alpha = TheGameEngine->getLogicTimeAccumulator() * TheFramePacer->getActualLogicTimeScaleFps();


My understanding is that this is a value between 0 and 1 to tell how far the current sub frame has advanced before it reaches the next logic frame.

It would be nice to abstract this concept in the FramePacer because it can be useful in many places. For that the GameEngine needs to give it information every render update.

xezon · 2026-08-02T09:18:03Z

+
+		m_visualExtrapolationMtx = m_prevLogicMtx;
+
+		if (fabs(angleDelta) > 0.001f && fabs(angleDelta) < 3.0f)


What is this angle limit for?

xezon · 2026-08-02T09:25:10Z

-					ai->getTurretRotAndPitch((WhichTurretType)tslot, &turretAngle, &turretPitch);
-			}
+			Real angleDelta = stdAngleDiff(m_currTurretAngle[tslot], m_prevTurretAngle[tslot]);
+			Real interpTurretAngle = m_prevTurretAngle[tslot] + angleDelta * clampAlpha;


interpolatedTurretAngle

xezon · 2026-08-02T09:26:41Z

+	const AIUpdateInterface* ai = obj ? obj->getAIUpdateInterface() : nullptr;
+	UnsignedInt currentLogicFrame = TheGameLogic ? TheGameLogic->getFrame() : 0;
+
+	if (currentLogicFrame != m_lastTurretSampledFrame)


Can move this portion into a new function to tidy up and give it a name.

xezon · 2026-08-02T09:27:28Z

+
+	UnsignedInt currentLogicFrame = TheGameLogic->getFrame();
+
+	if (currentLogicFrame != m_lastSampledLogicFrame)


Can move this portion into a new function to tidy up and give it a name.

xezon · 2026-08-04T08:31:20Z

+
+		if (fabs(angleDelta) > 0.001f && fabs(angleDelta) < 3.0f)
+		{
+			m_visualExtrapolationMtx.In_Place_Pre_Rotate_Z(angleDelta * clampAlpha);


If I am reading this right this only predicts rotation on Z axis. I think this should Slerp with Quaternion to rotate all axis. Using Quaternion, because that should yield better interpolation than the Matrix does.

https://www.youtube.com/watch?v=sJcVJEOwLUs

Caball009

There are quite a number of variables in the new code that can be marked as const. I think it wouldn't hurt to check for const correctness and change where possible.

Caball009 · 2026-08-06T01:32:08Z

+	for (i = 0; i < MAX_TURRETS; ++i)
+	{
+		m_prevTurretAngle[i] = 0.0f;
+		m_currTurretAngle[i] = 0.0f;
+		m_prevTurretPitch[i] = 0.0f;
+		m_currTurretPitch[i] = 0.0f;
+	}


Could do this instead:

std::fill(m_prevTurretAngle, m_prevTurretAngle + ARRAY_SIZE(m_prevTurretAngle), 0.0f); std::fill(m_currTurretAngle, m_currTurretAngle + ARRAY_SIZE(m_currTurretAngle), 0.0f); std::fill(m_prevTurretPitch, m_prevTurretPitch + ARRAY_SIZE(m_prevTurretPitch), 0.0f); std::fill(m_currTurretPitch, m_currTurretPitch + ARRAY_SIZE(m_currTurretPitch), 0.0f);

githubawn changed the title ~~bugfix(drawable): Decouple projectile logic position from visual render update~~ bugfix(drawable): Decouple the visual render from the projectile logic position Apr 13, 2026

githubawn changed the title ~~bugfix(drawable): Decouple the visual render from the projectile logic position~~ bugfix(drawable): Decouple visual render from projectile's logic position Apr 13, 2026

Mauller reviewed Apr 13, 2026

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Comment thread GeneralsMD/Code/GameEngine/Source/GameClient/Drawable.cpp

xezon reviewed Apr 13, 2026

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xezon added the Experimental Wear safety goggles in lab label Apr 13, 2026

githubawn marked this pull request as draft April 14, 2026 11:48

githubawn added 7 commits August 1, 2026 01:20

Decouple projectile logic position from visual render update

860c5ca

removed unused oldpos

98b3aa8

use explicit construction and fix alignment

d8a0f50

prepared applySubFrameExtrapolation for future decoupling

e6e65a6

fix NeutronMissileUpdate overcompensation at start of launch

47cc961

added caching

cb85b4d

refactor(Drawable): implement automatic sub-frame interpolation for p…

0c3caf7

…osition, rotation, and turrets

githubawn force-pushed the bugfix/drawable-projectile-subframe-extrapolation branch from be62f3b to 0c3caf7 Compare July 31, 2026 23:53

githubawn marked this pull request as ready for review July 31, 2026 23:53

fix generals

55d8335

Skyaero42 reviewed Aug 2, 2026

View reviewed changes

xezon reviewed Aug 2, 2026

View reviewed changes

xezon reviewed Aug 4, 2026

View reviewed changes

Caball009 reviewed Aug 6, 2026

View reviewed changes


		m_visualExtrapolationMtx = m_prevLogicMtx;

		if (fabs(angleDelta) > 0.001f && fabs(angleDelta) < 3.0f)


		UnsignedInt currentLogicFrame = TheGameLogic->getFrame();

		if (currentLogicFrame != m_lastSampledLogicFrame)

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Greptile Summary

Confidence Score: 5/5

Important Files Changed

Sequence Diagram

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xezon Aug 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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githubawn commented Apr 13, 2026 •

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