Matrix Class (GDI+)

Overview

The Matrix class represents a 3×2 matrix used for geometric transformations in GDI+. It provides methods to translate, rotate, scale, and shear graphics objects.

Properties

• Elements – Gets or sets the six floating‑point values of the matrix.
• IsIdentity – Indicates whether the matrix is the identity matrix.
• IsInvertible – Indicates whether the matrix can be inverted.

Methods

• Translate(float dx, float dy, MatrixOrder order = MatrixOrder.Prepend)
• Rotate(float angle, MatrixOrder order = MatrixOrder.Prepend)
• Scale(float sx, float sy, MatrixOrder order = MatrixOrder.Prepend)
• Shear(float shearX, float shearY, MatrixOrder order = MatrixOrder.Prepend)
• Invert()
• TransformPoints(PointF[] pts)
• Multiply(Matrix matrix, MatrixOrder order = MatrixOrder.Prepend)

Examples

using System.Drawing;
using System.Drawing.Drawing2D;

Bitmap bmp = new Bitmap(300, 200);
using (Graphics g = Graphics.FromImage(bmp))
{
    Matrix m = new Matrix();
    m.Translate(150, 100);
    m.Rotate(45);
    g.Transform = m;

    g.FillEllipse(Brushes.CornflowerBlue, -50, -50, 100, 100);
    bmp.Save("rotated.png");
}

#include 
using namespace Gdiplus;
int main()
{
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, nullptr);

    Bitmap bitmap(300,200,PixelFormat32bppARGB);
    Graphics* g = Graphics::FromImage(&bitmap);
    Matrix m;
    m.Translate(150,100);
    m.Rotate(45);
    g->SetTransform(&m);
    g->FillEllipse(&SolidBrush(Color::Blue), -50,-50,100,100);
    bitmap.Save(L"rotated_cpp.png", &EncoderPNG, nullptr);

    delete g;
    GdiplusShutdown(gdiplusToken);
    return 0;
}

Remarks

When concatenating transformations, the order of operations matters. Use MatrixOrder.Prepend to apply a new transformation before the existing one, or MatrixOrder.Append to apply it after.