Shows a definite integral as a Riemann-sum approximation with rectangles whose count increases toward a limit, highlighting dx as the rectangle width. The lower panel shows the indefinite integral as an antiderivative family F(x)+C, and animates the Fundamental Theorem of Calculus by comparing F(b) and F(a) so their difference matches the accumulated area.
Pure Canvas2D. Responsive scaling via scale=min(w,h)/240 and grid snapping for a blocky look. Time-based animation cycles: N ramps 4→32 for Riemann rectangles; a sweeping highlight shows dx. Antiderivative family uses multiple curves with animated constant C; FTC panel animates b sliding and displays F(b)-F(a).