Objective
Improve the quality of dynamics driven by velocity input.
Related Links
- Branches: Artbox and feature-velocity-compression
Design Revisions
| Revision | Current Design | Issues | Changes |
|---|---|---|---|
| 1. Velocity mapping | Velocity is clamped to a limit | The users input motion velocity is clipped at an arbitrary value. Strokes lack a realistic sense of motion. | Add a compress_velocity function for logarithmic velocity normalization. Lower speeds are more sensitive, faster motions are compressed rather than clamped, this gives a more natural feel. Also removes a subtle filtering artifact. |
Notes
Uses a log function, no discernable slowdown on a fast pc.
Without Feature: Left side is a slow to fast stroke, right side has inverted velocity mapping
With Feature: Left side is a slow to fast stroke, right side has inverted velocity mapping
MR Description
This feature improves the velocity handling in gimpmotionbuffer.c by implementing a logarithmic velocity compression function and refining the smoothing algorithm. The key changes and their benefits are:
Changes
Logarithmic Velocity Compression:
- Introduces a new compression function that maps raw velocities to a compressed range using a logarithmic scale.
- Enhances sensitivity for low velocities, allowing for finer control during slow movements.
- Prevents compressed velocities from saturating too quickly at high raw velocities, ensuring a smooth transition across the velocity spectrum.
Improved Smoothing Mechanism:
- Utilizes a consistent exponential smoothing factor in the velocity calculations.
- Provides stable and smooth transitions by reducing abrupt changes in velocity.
- Ensures the smoothed velocity is correctly maintained for accurate computations in subsequent events.
Optimizations and Refactoring:
- Adds precomputed constants for logarithmic calculations to optimize performance.
- Refactors code to correctly update
buffer->last_coords.velocityafter assignments to prevent unintended overwrites. - Includes detailed comments explaining the purpose of constants like
V_MAX,k, andV_THRESHOLD, aiding future maintenance and readability.
Benefit
These enhancements result in more responsive and natural tool dynamics within GIMP’s drawing tools, offering users improved control and a better overall experience when interacting with dynamic brushes and other velocity-dependent features.