[BUG-3960] [MAINTENANCE RC] Ribbon particles using textures containing alpha flash white at certain camera angles

Steps To Reproduce

Login on a viewer build that has the new ribbon paricles feature.
Rez 2 boxes, and link them together.

Save this script in the root prim:


   // Ribbon particle demo object, by Maestro Linden.  Spins around to demonstrate ribbon particles.
   // 1) Rez 2 boxes, and link them together
   // 2) Save this script in the root prim
   // 3) Particles using the ribbon mask are emitted from the child prim, as the root prim spins around.
   default
   {
       state_entry()
       {
           // particle texture to use
           key texture = "c73ca11d-57bf-d4bb-e87a-e5af6c64ae78";
           llSetLinkPrimitiveParamsFast(1, [PRIM_TEXTURE, ALL_SIDES, texture, <1,1,0>, ZERO_VECTOR, 0.0]);

           // spin the linkset
           llTargetOmega(<0,0,1>, 1, 1);
           // offset, rotate, and hide the child prim
           llSetLinkPrimitiveParams(2, [PRIM_ROT_LOCAL, <-0.55141, -0.02408, -0.03638, 0.83309>,
               PRIM_POS_LOCAL, <0.0, 1.0, 0.0>,
               PRIM_COLOR, ALL_SIDES, <0,0,0>, 0.0]);
           llLinkParticleSystem(2, [
               PSYS_SRC_PATTERN, PSYS_SRC_PATTERN_DROP,
               PSYS_PART_FLAGS, PSYS_PART_RIBBON_MASK|PSYS_PART_INTERP_COLOR_MASK,
               PSYS_PART_START_SCALE, <0.25, 2.0, 0.0>,
               PSYS_PART_START_ALPHA, 1.0,
               PSYS_PART_END_ALPHA, 0.0,
               PSYS_PART_MAX_AGE, 5.0,
               PSYS_SRC_TEXTURE, texture
           ]);
       }
   }

Observe how the ribbon particles look at different camera angles.

Observed Behaviour

At certain camera angles the ribbon particles will flash white.
The effect reproduces whether ALM is enabled (but shadows disabled) or disabled.
When shadows are enabled, the effect is much less severe though it does still happen.
Demo video: http://www.youtube.com/watch?v=z9MvSGlQHwM&hd=1
- On the video, the object on the left is using the above script. The object on the right is using the above script but with a fully alpha texture, UUID cf6ad464-6d7a-8079-850a-477062875bf6
Expected Behaviour

The ribbon particles should render correctly at all camera angles.

Links

Duplicates

[ ] https://github.com/secondlife/jira-archive/issues/13726

Original Jira Fields

| Field | Value | | ------------- | ------------- | | Issue | BUG-3960 | | Summary | [MAINTENANCE RC] Ribbon particles using textures containing alpha flash white at certain camera angles | | Type | Bug | | Priority | Unset | | Status | Accepted | | Resolution | Accepted | | Reporter | Whirly Fizzle (whirly.fizzle) | | Created at | 2013-09-23T10:03:12Z | | Updated at | 2014-10-13T14:40:44Z | ``` { 'Business Unit': ['Platform'], 'System': 'SL Viewer', 'Target Viewer Version': 'viewer-development', 'What just happened?': 'blah....', 'What were you doing when it happened?': '.', 'What were you expecting to happen instead?': '.', } ```

secondlife / jira-archive