Discussing the article: "Creating a Cairo-Inspired Graphics Library for MetaTrader 5 (Part 8): Paint, from Solid Colors to Gradients"

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Check out the new article: Creating a Cairo-Inspired Graphics Library for MetaTrader 5 (Part 8): Paint, from Solid Colors to Gradients.

Gradients are introduced by making the source a polymorphic paint: the rasterizer calls ColorAt(x, y) for each pixel. This enables solid, linear and radial fills on any path with a single inner‑loop change, keeping Path.mqh untouched. The article details color stops and padding, corner‑based normalization for linear gradients, normalized centers/radii for radial ones, a CCairoFillStyle handle, and compatibility with the legacy uint Fill().

Modern graphical interfaces rely on more than geometry and flat colors to communicate depth, hierarchy, and visual meaning. Buttons often have subtle vertical shading, cards use gentle color transitions to separate their sections, and focus indicators may appear as radial glows. In trading applications, the area beneath a price line can gradually fade into the background, while progress bars use color transitions to make their values easier to recognize. These effects are not merely decorative; they help create interfaces that are visually clear, intuitive, and consistent with modern software design.

To achieve these effects, a graphics library needs more than the ability to draw and fill shapes. It must also support gradients, allowing colors and transparency to vary smoothly across a surface rather than assigning a single flat color to every pixel.

In Part 7, we completed the geometry layer of our Cairo-inspired graphics library. It can now describe a wide range of shapes, including lines, polygons, thick strokes, cubic and quadratic Bézier curves, arcs, circles, ellipses, and rounded rectangles with independent corner radii. These shapes can be filled using either winding rule, with smooth edges and correct compositing. However, all rendering so far has relied on one flat color per shape.

In this article, we extend the rendering system to support gradients without significantly changing the existing architecture. Although gradient calculations themselves are relatively straightforward, the more interesting challenge is integrating them into the rendering pipeline efficiently and cleanly.

Author: Sandro Begashvili