Your question seems to have at least two sub-questions:
- Draw along a diagonal: your sample seems to indicate that you want to write each line of text perpendicularly to the secondary diagonal, so I will go with that.
- I assumed we are talking Rectangles, so the 45 degree part is just silly, added code to calculate the real angle
- Draw within a band I do not know if your problem is positioning or keeping a string width within the bounds.
The code below addresses the Draw along a diagonal part, to get the positioning part right. Fitting things in a "band" in my opinion is easier to address (you have to loop through with a g.MeasureString until things fit or wrap text, I do not know the exact requirements). Let me know if you need more clarification.
I've tried to include comments in the code, but let me know if anything needs clearing up.
I wish formatting code would be easier on SO...
public class DiagonalLines
{
private readonly Font font;
private readonly Brush brush = new SolidBrush(Color.Black);
private readonly Image image;
private readonly float width;
private readonly float height;
private readonly float diagonalAngle;
private readonly string savePath;
public DiagonalLines(string path, string savePath)
{
this.image = Image.FromFile(path);
width = image.Width;
height = image.Height;
//this could be optimized
//you want to write perpendicular to the secondary diagonal, if I understood correctly
//Math.Atan(height / width) => angle, in radians of the first diagonal
//after applying "-" we obtain the angle, in radians, of the secondary diagonal
//the rest of the first term is converting radians to degrees
diagonalAngle = -(float)(Math.Atan(height / width) * 180 / Math.PI) + /* perpendicular*/ 90;
this.font = new Font("Arial", (float)image.Width / 80); //write about 80 characters for a full horizontal text line
this.savePath = savePath;
}
public void DrawLines(params string[] lines)
{
using (Graphics g = Graphics.FromImage(image))
{
//M should be the largest character in most "western" fonts
var lineHeight = g.MeasureString("M", font).Height;
var halfTheLines = (float)lines.Length / 2; //about half the lines should be "above" the midpoint of the secondary diagonal
var offsetY = -(halfTheLines * lineHeight); //we scale the position against the line height
//same effect could probably be achieved with ScaleTransform
g.DrawLine(Pens.Red, 0, height, width, 0); //draw the secondary diagonal
foreach (var val in lines)
{
var size = g.MeasureString(val, font);
g.ResetTransform();
g.TranslateTransform(width / 2, height / 2); //go to center of image
g.RotateTransform(diagonalAngle);
//translate, to center the text and apply our offset
g.TranslateTransform(-size.Width / 2, -size.Height / 2 + offsetY);
g.DrawString(val, font, brush, 0, 0);
offsetY += lineHeight;
}
}
image.Save(savePath);
}
}
static void Main(string[] args)
{
var lines = new DiagonalLines("c:\\temp\\img\\poza.png", "c:\\temp\\img\\watermarked.jpg");
lines.DrawLines("this", "that", "the other", "and another");
Process.Start("c:\\temp\\img\\watermarked.jpg");
}
