Lecture Notes: Implementing DDA Line Algorithm using QT Creator

Project Setup

• Create a project named "DDA Line" in QT Creator (name can be customized).
• Project files include:
  • dda.cpp
  • main.cpp
  • dda.h
  • ddaline.ui

UI Form Setup

• Open the UI form to design the interface.
• Input Fields: Line Segment Coordinates
  • Labels for X1, Y1, X2, Y2
  • Plain Text Edit Boxes for each coordinate
• Push Button
  • Add a push button and rename it (e.g., "DDA").
  • Set up a click event for the button.

Setting Up Event Handlers

• Connect Click Event to Function
  • Right-click the push button, go to slot, and select the clicked event.
  • Redirects to the main CPP file (dda.cpp or main.cpp), where the function will be defined.

Coding the DDA Function

• Function Definition
  • void DDA(float x1, float y1, float x2, float y2)
  • Convert input values from text boxes to integers.
  • Example of converting text to integer:

    int x1 = ui->textEdit->toPlainText().toInt();
    

  • Retrieve values for X1, Y1, X2, Y2 similarly.
• Drawing a Pixel
  • Example of setting a pixel: image.setPixel(50, 50, qRgb(255,255,255));
  • Use QLabel to display the result (label_5).

DDA Algorithm Implementation

1. Variables
   • int x, y
   • float deltaX, deltaY, length, xIncrement, yIncrement
2. Calculate Differences
   • deltaX = x2 - x1
   • deltaY = y2 - y1
3. Determine Length
   • Use the greater of abs(deltaX) or abs(deltaY) to determine length
4. Calculate Increments
   • xIncrement = deltaX / length
   • yIncrement = deltaY / length
5. Loop to Draw Line
   • Initialize x and y with x1, y1
   • Use a loop from 0 to length
   • Plot pixels using image.setPixel(x, y, qRgb(r, g, b))
   • Increment x and y by xIncrement and yIncrement
   • Example loop:

     for (int i = 0; i < length; i++) {
         image.setPixel(x, y, qRgb(255, 255, 255));
         x += xIncrement;
         y += yIncrement;
     }
     

Running the Project

• Build the project and ensure no errors.
• Run the project.
• Enter coordinates for the line segment (e.g., (100, 100) to (200, 200)).
• Click the DDA button to draw the line on the output screen.

Additional Information

• Output Screen
  • QLabel (label_5) used to display the drawn line.
  • Set QLabel size to 500x500.
• Color Customization
  • Change RGB values in setPixel to alter line color.

Summary

• Successfully implemented and ran the DDA line drawing algorithm in QT Creator.
• Interface allows user to input coordinates and draw the corresponding line segment using the DDA algorithm.
• Next steps could include implementing the Bresenham line algorithm similarly.

---