Question

just in pure gdi.
thoughts or code are all welcome.

Answer 1

Create a rounded rect as a path, select the path as the clipping path, then do a gradient fill of the same rectangle. Code with MFC would look like this:

int top = 10;
int left = 10;
int right = 200;
int bottom = 200;
int radius = 20;


pDC->BeginPath();
pDC->RoundRect(left, top, right, bottom, radius, radius);
pDC->EndPath();
pDC->SelectClipPath(RGN_COPY);

TRIVERTEX vertices[2];

vertices[0].x = left;
vertices[0].y = top;
vertices[0].Red = 0xffff;
vertices[0].Green = 0;
vertices[0].Blue = 0;
vertices[0].Alpha = 0xffff;

vertices[1].x = right;
vertices[1].y = bottom;
vertices[1].Red = 0;
vertices[1].Green = 0;
vertices[1].Blue = 0xffff;
vertices[1].Alpha = 0xffff;

GRADIENT_RECT r;
r.UpperLeft = 0;
r.LowerRight = 1;

pDC->GradientFill(vertices, 2, &r, 1, GRADIENT_FILL_RECT_V);

If you’re not using MFC, the pDC->x(...) would be replaced with x(your_DC, ...).