AutoLISP Tutorial 1: Design Your Own Circle Drawer

Welcome to this AutoLISP program tutorial where we embark on a journey to create a user-centric function for drawing circles in AutoCAD. Whether you’re a seasoned programmer or someone just dipping their toes into the world of AutoLISP, this guide is crafted with simplicity in mind. We’ll delve into the step-by-step process, ensuring you grasp the logic behind each line of code without feeling overwhelmed. By the end, you’ll have a functional tool at your disposal and a deeper understanding of how AutoLISP interacts with AutoCAD.

Objective Your task is to craft a function in AutoLISP that allows users to draw circles in AutoCAD with specific attributes.

Task Breakdown

1. Function Creation: Begin by defining a function that you will later fill with instructions.
2. User Interaction: Ensure the function asks the user for three pieces of information:
   • The diameter they desire for their circle.
   • The name of the layer they want their circle to be placed on.
   • The point on the screen where the center of the circle should be located.
3. Layer Handling: If the layer given by the user isn’t available, create a new one. This new layer should have a distinct color – red.
4. Drawing Execution: With the collected details, instruct AutoCAD to sketch a circle with the chosen diameter at the selected center point, all while being on the desired layer.
5. Optimal User Experience: Before starting any operations, ensure that the usual command prompts that appear in AutoCAD’s command line are hidden. This gives a neater appearance. Once your function finishes its tasks, those prompts should return to their normal behavior.

Guidance

• Carefully consider the order of your instructions within the function.
• Always pay attention to the details given by the user. Their choices should directly influence the resulting circle.
• After you believe you’ve completed the function, put it to the test. Try drawing several circles to ensure it behaves as expected.

Upon finishing the tutorial, submit your design. Remember, clarity in your function and attention to detail are key.

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AutoLISP Tutorial 1 Solution: Designing a Circle Drawer in AutoCAD

The objective of this exercise was to provide a comprehensive function that allows users to define and draw circles in AutoCAD. This involves collecting user inputs, handling layers, and drawing a circle. Let’s dive into the solution and understand the logic behind each instruction.

The Complete Program

Line-by-Line Explanation

(defun drawcircle ( ): This line starts the definition of a new function called drawcircle. The function does not take any arguments.

(setq svcm (getvar “cmdecho”)): Here, we’re saving the current state (on or off) of the command echo to a variable called svcm. This will allow us to restore this setting at the end of our function.

(setvar “cmdecho” 0): This command turns off the command echo, which means any commands executed after this will not be shown in the command line, offering a cleaner user experience.

(setq dia1 (getreal “\nEnter diameter of circle: “)): We’re prompting the user to input the diameter of the circle. The value entered by the user is stored in the variable dia1.

(setq layn (getstring “\nEnter Layer name: “)): This line asks the user for the name of the layer where they want their circle to be placed. The provided name is stored in the variable layn.

(setq pnt1 (getpoint “\nEnter the center point for circle: “)): The user is prompted to select a point on the screen, which will be used as the center of the circle. This point is stored in the variable pnt1.

(command “-LAYER” “m” layn “c” “red” layn “”): Using this command, we’re managing layer settings. If the layer with the name stored in layn doesn’t exist, it’s created. Additionally, its color is set to red.

(command “CIRCLE” pnt1 dia1): With this line, we’re commanding AutoCAD to draw a circle. We’re using the point stored in pnt1 as its center and the value in dia1 as its diameter.

(setvar “cmdecho” svcm): Here, we’re restoring the command echo to its original state (either on or off) which was saved at the start in the svcm variable.

(princ): This is the concluding line of our function. It’s a standard way to gracefully exit a function in AutoLISP, ensuring no stray values are printed in the command line upon completion.

Conclusion

Congratulations on successfully navigating through this tutorial! You’ve now equipped yourself with a practical tool and, more importantly, a foundational understanding of how AutoLISP functions are structured and executed within AutoCAD. Remember, the journey of coding is filled with continuous learning. Use this function as a stepping stone and challenge yourself to explore more complex creations.