Difference between fillTriangle_cont and fillTriangle

[brightproject]

Good day @sumotoy
When drawing a filled cube, fillQuad is used.
Its function uses fillTriangle_cont function to draw filled triangles.
What is the difference between fillTriangle_cont and fillTriangle?
When I use the code, my filled cube ripples.
With wireframe no problem.
Stm32 controller, ST7735 display.

solid_body_filled.mp4

solid_body_wireframe.mp4