BrightContrast not working correctly with negative contrast

followup to rB8dd95abb2ff9 (which fixed this for the Compositor node),
turns out this was also wrong for the VSE modifier and in vertex color
operator.

- also adjust min/max for VSE modifier
- also guard against division by zero

Reviewers: brecht

Maniphest Tasks: T67808

Differential Revision: https://developer.blender.org/D5398

1 files changed, 3 insertions, 2 deletions

diff --git a/source/blender/compositor/operations/COM_BrightnessOperation.cpp b/source/blender/compositor/operations/COM_BrightnessOperation.cpp
index d0bab5aa4d9..b6c22029899 100644
--- a/source/blender/compositor/operations/COM_BrightnessOperation.cpp
+++ b/source/blender/compositor/operations/COM_BrightnessOperation.cpp
@@ -62,12 +62,13 @@ void BrightnessOperation::executePixelSampled(float output[4],
    * Extracted of OpenCV demhist.c
    */
   if (contrast > 0) {
-    a = 1.0f / (1.0f - delta * 2.0f);
+    a = 1.0f - delta * 2.0f;
+    a = 1.0f / max_ff(a, FLT_EPSILON);
     b = a * (brightness - delta);
   }
   else {
     delta *= -1;
-    a = 1.0f - delta * 2.0f;
+    a = max_ff(1.0f - delta * 2.0f, 0.0f);
     b = a * brightness + delta;
   }
   if (this->m_use_premultiply) {