add basic 2d triangle rendering

only solid color support so far. and using an un-optimized algorithm

ggdt/src/graphics/bitmap/mod.rs

@@ -12,6 +12,7 @@ pub mod pcx;
 pub mod png;
 pub mod primitives;
 pub mod rgb;
+pub mod triangles;
 
 #[derive(Error, Debug)]
 pub enum BitmapError {

ggdt/src/graphics/bitmap/triangles.rs

@@ -0,0 +1,71 @@
+use crate::graphics::bitmap::Bitmap;
+use crate::graphics::Pixel;
+use crate::math::vector2::Vector2;
+
+#[inline]
+fn cross(a: Vector2, b: Vector2, c: Vector2) -> f32 {
+	(c.x - a.x) * (b.y - a.y) - (c.y - a.y) * (b.x - a.x)
+}
+
+impl<PixelType: Pixel> Bitmap<PixelType> {
+	pub fn triangle_2d_solid_color(&mut self, a: Vector2, b: Vector2, c: Vector2, color: PixelType) {
+		self.triangle_2d_custom(
+			a, //
+			b,
+			c,
+			|dest_pixels, _w0, _w1, _w2| unsafe {
+				*dest_pixels = color;
+			},
+		)
+	}
+
+	#[inline]
+	pub fn triangle_2d_custom(
+		&mut self,
+		a: Vector2,
+		b: Vector2,
+		c: Vector2,
+		pixel_fn: impl Fn(*mut PixelType, f32, f32, f32),
+	) {
+		// based off the triangle rasterization algorithm presented in these article series' (as well as others)
+		// https://fgiesen.wordpress.com/2013/02/17/optimizing-sw-occlusion-culling-index/
+		// https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/rasterization-stage.html
+		// https://kitsunegames.com/post/development/2016/07/28/software-3d-rendering-in-javascript-pt2/
+
+		// TODO: optimize further. have had some trouble with some explanations of the optmizations presented in the
+		//       linked article and the math presented. in particular i would prefer to have counter-clockwise vertex
+		//       ordering but the math presented seems to only work as-is with clockwise ordering ... *grumble*
+		// TODO: implement fill rules, probably using top-left ordering as most 3d APIs do i guess
+
+		let min_x = a.x.min(b.x).min(c.x);
+		let min_y = a.y.min(b.y).min(c.y);
+		let max_x = a.x.max(b.x).max(c.x);
+		let max_y = a.y.max(b.y).max(c.y);
+
+		let min_x = std::cmp::max(self.clip_region().x, min_x as i32);
+		let min_y = std::cmp::max(self.clip_region().y, min_y as i32);
+		let max_x = std::cmp::min(self.clip_region().right(), max_x as i32);
+		let max_y = std::cmp::min(self.clip_region().bottom(), max_y as i32);
+
+		let draw_width = (max_x - min_x + 1) as usize;
+		let next_row_inc = self.width() as usize;
+		let mut pixels = unsafe { self.pixels_at_mut_ptr_unchecked(min_x, min_y) };
+
+		for y in min_y..=max_y {
+			let row_pixels = unsafe { std::slice::from_raw_parts_mut(pixels, draw_width) };
+			for (idx, pixel) in row_pixels.iter_mut().enumerate() {
+				let x = min_x + idx as i32;
+
+				let p = Vector2::new(x as f32, y as f32);
+				let w0 = cross(b, c, p);
+				let w1 = cross(c, a, p);
+				let w2 = cross(a, b, p);
+
+				if w0 >= 0.0 && w1 >= 0.0 && w2 >= 0.0 {
+					pixel_fn(pixel, w0, w1, w2);
+				}
+			}
+			pixels = unsafe { pixels.add(next_row_inc) };
+		}
+	}
+}

ggdt/src/graphics/prelude.rs

@@ -10,6 +10,7 @@ pub use crate::graphics::{
 		png::*,
 		primitives::*,
 		rgb::{blit::*, primitives::*, *},
+		triangles::*,
 		*,
 	},
 	bitmapatlas::*,