Hello, I am wanting to write a math/physics book or possibly a PDF online book and I'm wondering if anyone knows of any programs that exists for making pictures and drawing diagrams. I not just looking for something to make x-y graphs or 3-D graphs, I'm looking for something that designed for custom problems like drawing a truck driving down a hill or a person throwing a baseball. Do the people who make the texts books use programs to make drawing these things easier? Or do they just use like photoshop or some vector based program and then import that image into the actual text book. Thanks.