diff --git a/ggdt/src/graphics/bitmap/primitives.rs b/ggdt/src/graphics/bitmap/primitives.rs
index 880cbb1..adc78c9 100644
--- a/ggdt/src/graphics/bitmap/primitives.rs
+++ b/ggdt/src/graphics/bitmap/primitives.rs
@@ -20,6 +20,19 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		}
 	}
 
+	/// Sets the pixel at the given coordinates to the color returned by the given function. The
+	/// given function is one that accepts a color value that corresponds to the current pixel
+	/// at the given coordinates. If the coordinates lie outside of the bitmaps clipping region,
+	/// no pixels will be changed and the given pixel function will not be called.
+	#[inline]
+	pub fn set_custom_pixel(&mut self, x: i32, y: i32, pixel_fn: impl Fn(PixelType) -> PixelType) {
+		unsafe {
+			if let Some(pixels) = self.pixels_at_mut_ptr(x, y) {
+				*pixels = pixel_fn(*pixels);
+			}
+		}
+	}
+
 	/// Sets the pixel at the given coordinates to the color specified. The coordinates are not
 	/// checked for validity, so it is up to you to ensure they lie within the bounds of the
 	/// bitmap.
@@ -29,6 +42,16 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		*p = color;
 	}
 
+	/// Sets the pixel at the given coordinates to the color returned by the given function. The
+	/// given function is one that accepts a color value that corresponds to the current pixel at
+	/// the given coordinates. The coordinates are not checked for validity, so it is up to you to
+	/// ensure they lie within the bounds of the bitmap.
+	#[inline]
+	pub unsafe fn set_custom_pixel_unchecked(&mut self, x: i32, y: i32, pixel_fn: impl Fn(PixelType) -> PixelType) {
+		let p = self.pixels_at_mut_ptr_unchecked(x, y);
+		*p = pixel_fn(*p);
+	}
+
 	/// Gets the pixel at the given coordinates. If the coordinates lie outside of the bitmaps
 	/// clipping region, None is returned.
 	#[inline]
@@ -137,6 +160,68 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		}
 	}
 
+	pub fn line_custom(&mut self, x1: i32, y1: i32, x2: i32, y2: i32, pixel_fn: impl Fn(PixelType) -> PixelType) {
+		let mut dx = x1;
+		let mut dy = y1;
+		let delta_x = x2 - x1;
+		let delta_y = y2 - y1;
+		let delta_x_abs = delta_x.abs();
+		let delta_y_abs = delta_y.abs();
+		let delta_x_sign = delta_x.signum();
+		let delta_y_sign = delta_y.signum();
+		let mut x = delta_x_abs / 2;
+		let mut y = delta_y_abs / 2;
+		let offset_x_inc = delta_x_sign;
+		let offset_y_inc = delta_y_sign * self.width as i32;
+
+		unsafe {
+			// safety: while we are blindly getting a pointer to this x/y coordinate, we don't
+			// write to it unless we know the coordinates are in bounds.
+			// TODO: should be ok ... ? or am i making too many assumptions about memory layout?
+			let mut dest = self.pixels_at_mut_ptr_unchecked(x1, y1);
+
+			if self.is_xy_visible(dx, dy) {
+				*dest = pixel_fn(*dest);
+			}
+
+			if delta_x_abs >= delta_y_abs {
+				for _ in 0..delta_x_abs {
+					y += delta_y_abs;
+
+					if y >= delta_x_abs {
+						y -= delta_x_abs;
+						dy += delta_y_sign;
+						dest = dest.offset(offset_y_inc as isize);
+					}
+
+					dx += delta_x_sign;
+					dest = dest.offset(offset_x_inc as isize);
+
+					if self.is_xy_visible(dx, dy) {
+						*dest = pixel_fn(*dest);
+					}
+				}
+			} else {
+				for _ in 0..delta_y_abs {
+					x += delta_x_abs;
+
+					if x >= delta_y_abs {
+						x -= delta_y_abs;
+						dx += delta_x_sign;
+						dest = dest.offset(offset_x_inc as isize);
+					}
+
+					dy += delta_y_sign;
+					dest = dest.offset(offset_y_inc as isize);
+
+					if self.is_xy_visible(dx, dy) {
+						*dest = pixel_fn(*dest);
+					}
+				}
+			}
+		}
+	}
+
 	/// Draws a horizontal line from x1,y to x2,y.
 	pub fn horiz_line(&mut self, x1: i32, x2: i32, y: i32, color: PixelType) {
 		let mut region = Rect::from_coords(x1, y, x2, y);
@@ -150,6 +235,18 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		}
 	}
 
+	pub fn horiz_line_custom(&mut self, x1: i32, x2: i32, y: i32, pixel_fn: impl Fn(PixelType) -> PixelType) {
+		let mut region = Rect::from_coords(x1, y, x2, y);
+		if region.clamp_to(&self.clip_region) {
+			unsafe {
+				let dest = &mut self.pixels_at_mut_unchecked(region.x, region.y)[0..region.width as usize];
+				for pixel in dest.iter_mut() {
+					*pixel = pixel_fn(*pixel);
+				}
+			}
+		}
+	}
+
 	/// Draws a vertical line from x,y1 to x,y2.
 	pub fn vert_line(&mut self, x: i32, y1: i32, y2: i32, color: PixelType) {
 		let mut region = Rect::from_coords(x, y1, x, y2);
@@ -164,6 +261,19 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		}
 	}
 
+	pub fn vert_line_custom(&mut self, x: i32, y1: i32, y2: i32, pixel_fn: impl Fn(PixelType) -> PixelType) {
+		let mut region = Rect::from_coords(x, y1, x, y2);
+		if region.clamp_to(&self.clip_region) {
+			unsafe {
+				let mut dest = self.pixels_at_mut_ptr_unchecked(region.x, region.y);
+				for _ in 0..region.height {
+					*dest = pixel_fn(*dest);
+					dest = dest.add(self.width as usize);
+				}
+			}
+		}
+	}
+
 	/// Draws an empty box (rectangle) using the points x1,y1 and x2,y2 to form the box to be
 	/// drawn, assuming they are specifying the top-left and bottom-right corners respectively.
 	pub fn rect(&mut self, mut x1: i32, mut y1: i32, mut x2: i32, mut y2: i32, color: PixelType) {
@@ -229,6 +339,91 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		}
 	}
 
+	pub fn rect_custom(
+		&mut self,
+		mut x1: i32,
+		mut y1: i32,
+		mut x2: i32,
+		mut y2: i32,
+		pixel_fn: impl Fn(PixelType) -> PixelType
+	) {
+		// note: need to manually do all this instead of just relying on Rect::from_coords (which
+		// could otherwise figure all this out for us) mainly just because we need the post-swap
+		// x1,y1,x2,y2 values for post-region-clamping comparison purposes ...
+		if x2 < x1 {
+			swap(&mut x1, &mut x2);
+		}
+		if y2 < y1 {
+			swap(&mut y1, &mut y2);
+		}
+		let mut region = Rect {
+			x: x1,
+			y: y1,
+			width: (x2 - x1 + 1) as u32,
+			height: (y2 - y1 + 1) as u32,
+		};
+		if !region.clamp_to(&self.clip_region) {
+			return;
+		}
+
+		// we want to draw the top and bottom lines 1 pixel shorter at both ends to avoid overdrawing the
+		// corners of the rect. this is mostly important for blended drawing operations.
+		// if the region's left and/or right x coordinate was NOT clipped, we chop off 1 pixel from either/both
+		// to avoid corner overdraw. if either/both of these x coordinates WAS clipped, we don't need to adjust that
+		// side, as no corner overdraw is possible in that case.
+		let mut horiz_draw_x = region.x;
+		let mut horiz_draw_width = region.width;
+		if x1 == region.x {
+			horiz_draw_x += 1;
+			horiz_draw_width -= 1;
+		}
+		if x2 == region.right() {
+			horiz_draw_width -= 1;
+		}
+
+		// top line, only if y1 was originally within bounds
+		if y1 == region.y {
+			unsafe {
+				let dest = &mut self.pixels_at_mut_unchecked(horiz_draw_x, region.y)[0..horiz_draw_width as usize];
+				for pixel in dest.iter_mut() {
+					*pixel = pixel_fn(*pixel);
+				}
+			}
+		}
+
+		// bottom line, only if y2 was originally within bounds
+		if y2 == region.bottom() {
+			unsafe {
+				let dest = &mut self.pixels_at_mut_unchecked(horiz_draw_x, region.bottom())[0..horiz_draw_width as usize];
+				for pixel in dest.iter_mut() {
+					*pixel = pixel_fn(*pixel);
+				}
+			}
+		}
+
+		// left line, only if x1 was originally within bounds
+		if x1 == region.x {
+			unsafe {
+				let mut dest = self.pixels_at_mut_ptr_unchecked(region.x, region.y);
+				for _ in 0..region.height {
+					*dest = pixel_fn(*dest);
+					dest = dest.add(self.width as usize);
+				}
+			}
+		}
+
+		// right line, only if x2 was originally within bounds
+		if x2 == region.right() {
+			unsafe {
+				let mut dest = self.pixels_at_mut_ptr_unchecked(region.right(), region.y);
+				for _ in 0..region.height {
+					*dest = pixel_fn(*dest);
+					dest = dest.add(self.width as usize);
+				}
+			}
+		}
+	}
+
 	/// Draws a filled box (rectangle) using the points x1,y1 and x2,y2 to form the box to be
 	/// drawn, assuming they are specifying the top-left and bottom-right corners respectively.
 	pub fn filled_rect(&mut self, x1: i32, y1: i32, x2: i32, y2: i32, color: PixelType) {
@@ -249,6 +444,31 @@ impl<PixelType: Pixel> Bitmap<PixelType> {
 		}
 	}
 
+	pub fn filled_rect_custom(
+		&mut self,
+		x1: i32,
+		y1: i32,
+		x2: i32,
+		y2: i32,
+		pixel_fn: impl Fn(PixelType) -> PixelType
+	) {
+		let mut region = Rect::from_coords(x1, y1, x2, y2);
+		if region.clamp_to(&self.clip_region) {
+			unsafe {
+				let mut dest = self.pixels_at_mut_ptr_unchecked(region.x, region.y);
+				for _ in 0..region.height {
+					// write the pixels horizontally for the entire width
+					for x in 0..region.width as isize {
+						let dest_x = dest.offset(x);
+						*dest_x = pixel_fn(*dest_x);
+					}
+					// move original pointer to the next row
+					dest = dest.add(self.width as usize);
+				}
+			}
+		}
+	}
+
 	/// Draws the outline of a circle formed by the center point and radius given.
 	pub fn circle(&mut self, center_x: i32, center_y: i32, radius: u32, color: PixelType) {
 		// TODO: optimize