Add the Gaussian function to blur a pixmap

[weihsinyeh]

Use Pascal's Triangle to approximate a 5x5 Gaussian Kernel, and apply Gaussian blur on the twin_pixmap_t to implement the blurring technique.

See: #34

[jserv]

• The original

• The proposed change

The idea behind #34 is to implement drop shadow, one of the most popular visual effects in modern window systems and compositing window managers. The effect should be applied at the window management level, not to background images, meaning the background image should not be blurred. The graphical effect of a visually elevated shape with a shadow underneath the window frame should occur transparently.

[weihsinyeh]

The idea behind #34 is to implement drop shadow, one of the most popular visual effects in modern window systems and compositing window managers. The effect should be applied at the window management level, not to background images, meaning the background image should not be blurred. The graphical effect of a visually elevated shape with a shadow underneath the window frame should occur transparently.

Because I'm still unsure where to place the blur operation, whether to implement the blur in '_twin_widget_queue_paint()', as this function handles the rendering order of each widget object. It would need to read the corresponding pixel block currently on the screen during rendering to blur the current background. Or should I implement this operation when each widget's TwinEventPaint occurs? So I first try to implement this function on the background to see its effect.

[jserv]

Or should I implement this operation when each widget's TwinEventPaint occurs? So I first try to implement this function on the background to see its effect.

Alternatively, you can write an image viewer with drop shadow functionality to evaluate performance and visual effects in the initial stage. Once you have a better understanding of the window manager events and their flow, we can proceed with integrating it into the window system.

See MDN: drop-shadow

[jserv]

Alternatively, you can write an image viewer with drop shadow functionality to evaluate performance and visual effects in the initial stage.

For performance evaluation, you may consider the code mentioned in #55 (comment) .

[weihsinyeh]

I haven't applied stack blur to the drop shadow yet, because I don't know how to access the current screen's topmost pixel map. I want to apply the stack blur to a specific region of the topmost pixel map that overlaps with the shadow and then use this as the new shadow. The topmost pixel map is efficiently updated by refreshing only the damaged areas.

[jserv]

Compilation error/warning reported by Clang:

src/window.c:72:13: error: non-void function 'twin_window_create' should return a value [-Wreturn-type]
   72 |             return;
      |             ^
src/window.c:65:17: warning: left operand of comma operator has no effect [-Wunused-value]
   65 |         window->shadow_offset_x, window->shadow_offset_y = 50, 50;
      |         ~~~~~~  ^~~~~~~~~~~~~~~
src/window.c:65:64: warning: expression result unused [-Wunused-value]
   65 |         window->shadow_offset_x, window->shadow_offset_y = 50, 50;
      |                    

[jserv]

I am unsure how to validate this. Could you provide the relevant procedures or methods along with the expected behavior?