Shows f(x) on the top panel with a moving upper limit x and blocky Riemann shading for the signed area ∫_a^x f(t)dt. The bottom panel graphs the accumulation function F(x) and draws a tangent whose slope dF/dx numerically matches the current f(x), illustrating FTC Part 1. A center annotation highlights FTC Part 2: ∫_a^b f(x)dx = F(b) − F(a).
Uses time-based sweep x=a→b with ease() for smooth motion. f(x) is sampled to scale axes; F(x) is computed each frame by a midpoint Riemann sum, and dF/dx is approximated with a centered finite difference. Rendering uses grid-snapped coordinates and Riemann bars for a retro blocky aesthetic on a black background with green highlights.