## Introduction

Most programmers used Windows SDK function `GradientFill`

to draw horizontal or vertical linear gradients or triangle gradients. Also, classes for diagonal gradients can be found on CodeProject. But what about custom gradients? Or experimental gradients? In this article, a class for drawing such gradients is presented. Its functionality is not hard-tested or free of bugs, so please have that in mind when using it.

## Background

One can find various articles on gradients all over the Internet and very good examples on CodeProject also.

## Using the code

To use the `CGradientRender`

class, include the provided header file *"GradientRender.h"* and make an instance of this class.

#include "GradientRender.h"
CGradientRender gradientRender;

Now, this class has only one public method called `DrawGradient`

, so call this method like in the example below:

RECT rect = {100, 100, 300, 300};
COLORREF startColor = RGB(0,0,255);
COLORREF endColor = RGB(255,0,0);
gradientRender.DrawGradient(hDC,rect,startColor,
endColor,GRADIENT_HORIZONTAL,TRANSFORMATION_NONE);

The last two arguments are the type of the gradient and the type of the transformation. If the type of the transformation is `TRANSFORMATION_NONE`

then this class can perform drawing of five basic gradient types:

- Horizontal gradient (
`GRADIENT_HORIZONTAL`

)
- Vertical gradient (
`GRADIENT_VERTICAL`

)
- Forward diagonal gradient (
`GRADIENT_FDIAGONAL`

)
- Backward diagonal gradient (
`GRADIENT_BDIAGONAL`

)
- Radial gradient (
`GRADIENT_RADIAL`

)

Also, using some type of transformation, the results can vary. This is the field of customization and experimenting. Current transformations are listed below:

- No transformation (
`TRANSFORMATION_NONE`

)
- Caricature transformation (
`TRANSFORMATION_CHARICATURE`

)
- Fisheye transformation (
`TRANSFORMATION_FISHEYE`

)
- Swirled transformation (
`TRANSFORMATION_SWIRLED`

)
- Cylinder transformation (
`TRANSFORMATION_CYLINDER`

)
- Shift transformation (
`TRANSFORMATION_SHIFT`

)

In basic, these six transformations are performed on five different types of gradients. There are 30 combinations for now. Some good, some even better. But, one must experiment with the parameters of the transformation in order to get custom results, or add a new transformation which would be the best. All transformations are performed in the private method `ApplyTransformation`

of the `CGradientRender`

class.

## Points of Interest

Working on this material, I found an interesting research field. Almost any image transformation can be applied here (even color transformation which is not tested here) and everyone is invited to try.