How to draw conic gradient?

General JUCE discussion
12

Here you go. It’s not the fastest implementation as it uses an intermediate image and fills every pixel but should work ok:

//==============================================================================
/** Fills and angle gradient.
    The gradient will start at -Pi radians (or 90 degrees to the left) and continue all the way round.
*/
inline void fillAngleGradient (Graphics& g, const ColourGradient& cg, Rectangle<int> bounds)
{
    Image img (Image::ARGB, bounds.getWidth(), bounds.getHeight(), false);
    const Image::BitmapData destData (img, Image::BitmapData::writeOnly);

    const float cx = (float) bounds.getCentreX();
    const float cy = (float) bounds.getCentreY();

    const float scale = (1.0f / (2.0f * MathConstants<float>::pi));

    HeapBlock<PixelARGB> lookup;
    const int numEntries = cg.createLookupTable (AffineTransform(), lookup);

    for (int y = 0; y < bounds.getHeight(); ++y)
    {
        for (int x = 0; x < bounds.getWidth(); ++x)
        {
            const float angleRadians = FastMathApproximations::atan2 (bounds.getY() + y - cy, bounds.getX() + x - cx);
            const float a = scale * (angleRadians + MathConstants<float>::pi);
            const int index = roundToInt (a * (numEntries - 1));
            jassert (isPositiveAndNotGreaterThan (a, 1.0f));
            jassert (isPositiveAndBelow (index, numEntries));

            destData.setPixelColour (x, y, lookup[index]);
        }
    }

    g.drawImageAt (img, bounds.getX(), bounds.getY());
}
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