Render a projected cube with the rasterization algos

ElHacker · Nov 28, 2019 · 2fa5335 · 2fa5335
1 parent b474610
commit 2fa5335
Show file tree

Hide file tree

Showing 2 changed files with 165 additions and 0 deletions.
diff --git a/raster-05.html b/raster-05.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html lang="en" dir="ltr">
+  <head>
+    <meta charset="utf-8">
+    <title>Raster 05</title>
+  </head>
+  <body>
+    <canvas id="canvas" width=600 height=600 style="border: 1px grey solid">
+    <script src="./raster-05.js" charset="utf-8"></script>
+  </body>
+</html>
diff --git a/raster-05.js b/raster-05.js
@@ -0,0 +1,154 @@
+
+// ======================================================================
+//  Low-level canvas access.
+// ======================================================================
+let canvas = document.getElementById('canvas');
+let canvas_context = canvas.getContext('2d');
+let canvas_buffer = canvas_context.getImageData(0, 0, canvas.width, canvas.height);
+let canvas_pitch = canvas_buffer.width * 4;
+
+
+let PutPixel = (x, y, color) => {
+  x = canvas.width / 2 + Math.floor(x);
+  y = canvas.height / 2 - Math.floor(y) - 1;
+
+  if (x < 0 || x >= canvas.width || y < 0 || y >= canvas.height) {
+    return;
+  }
+
+  let offset = 4 * x + canvas_pitch * y;
+  canvas_buffer.data[offset++] = color[0];
+  canvas_buffer.data[offset++] = color[1];
+  canvas_buffer.data[offset++] = color[2];
+  canvas_buffer.data[offset++] = 255; // Alpha = 255 (full opacity)
+}
+
+
+// Displays the contents of the offscreen buffer into the canvas.
+let UpdateCanvas = () => {
+  canvas_context.putImageData(canvas_buffer, 0, 0);
+}
+
+// ======================================================================
+//  Linear algebra and helpers.
+// ======================================================================
+
+// Computes scalar by vector multiplication
+var Multiply = function(k, vec) {
+  return [k*vec[0], k*vec[1], k*vec[2]];
+}
+
+
+// ======================================================================
+//  Rasterization code.
+// ======================================================================
+
+// Scene setup.
+const viewport_size = 1;
+const projection_plane_z = 1;
+
+// A Point representation.
+let Pt = function(x, y, h) {
+  if (!(this instanceof Pt)) {
+    return new Pt(x, y, h);
+  }
+
+  this.x = x;
+  this.y = y;
+  this.h = h;
+}
+
+// A 3D vertex
+let Vertex = function(x, y, z) {
+  if (!(this instanceof Vertex)) {
+    return new Vertex(x, y, z);
+  }
+
+  this.x = x;
+  this.y = y;
+  this.z = z;
+}
+
+let Interpolate = (i0, d0, i1, d1) => {
+  if (i0 == i1) {
+    return [d0];
+  }
+
+  let values = [];
+  const a = (d1 - d0) / (i1 - i0);
+  let d = d0;
+  for (let i = i0; i <= i1; i++) {
+    values.push(d);
+    d += a;
+  }
+
+  return values;
+}
+
+let DrawLine = (p0, p1, color) => {
+  let dx = p1.x - p0.x;
+  let dy = p1.y - p0.y;
+
+  if (Math.abs(dx) > Math.abs(dy)) {
+    // The line is horizontal-ish. Make sure it's left to right.
+    if (dx < 0) {
+      [p0, p1] = [p1, p0];
+    }
+
+    // Compute the Y values and draw.
+    let ys = Interpolate(p0.x, p0.y, p1.x, p1.y);
+    for (let x = p0.x; x <= p1.x; x++) {
+      // Using bitwise "or" | operator with 0 here is to remove the fractional part of the index.
+      PutPixel(x, ys[(x - p0.x) | 0], color);
+    }
+  } else {
+    // The line is vertical-ish. Make sure it's bottom to top.
+    if (dy < 0) {
+      [p0, p1] = [p1, p0];
+    }
+
+    // Compute the X values and draw.
+    let xs = Interpolate(p0.y, p0.x, p1.y, p1.x);
+    for (let y = p0.y; y <= p1.y; y++) {
+      // Using bitwise "or" | operator with 0 here is to remove the fractional part of the index.
+      PutPixel(xs[(y - p0.y) | 0], y, color);
+    }
+  }
+}
+
+// Converts 2D viewport coordinates to 2D canvas coordinates.
+let ViewportToCanvas = (p2d) => {
+  return Pt(p2d.x * canvas.width / viewport_size,
+            p2d.y * canvas.height / viewport_size);
+}
+
+let ProjectVertex = (v) => {
+  return ViewportToCanvas(Pt(v.x * projection_plane_z / v.z,
+                             v.y * projection_plane_z / v.z));
+}
+
+let vA = Vertex(-2, -0.5, 5);
+let vB = Vertex(-2, 0.5, 5);
+let vC = Vertex(-1, 0.5, 5);
+let vD = Vertex(-1, -0.5, 5);
+let vAb = Vertex(-2, -0.5, 6);
+let vBb = Vertex(-2, 0.5, 6);
+let vCb = Vertex(-1, 0.5, 6);
+let vDb = Vertex(-1, -0.5, 6);
+let RED = [255, 0, 0];
+let GREEN = [0, 255, 0];
+let BLUE = [0, 0, 255];
+DrawLine(ProjectVertex(vA), ProjectVertex(vB), BLUE);
+DrawLine(ProjectVertex(vB), ProjectVertex(vC), BLUE);
+DrawLine(ProjectVertex(vC), ProjectVertex(vD), BLUE);
+DrawLine(ProjectVertex(vD), ProjectVertex(vA), BLUE);
+DrawLine(ProjectVertex(vAb), ProjectVertex(vBb), RED);
+DrawLine(ProjectVertex(vBb), ProjectVertex(vCb), RED);
+DrawLine(ProjectVertex(vCb), ProjectVertex(vDb), RED);
+DrawLine(ProjectVertex(vDb), ProjectVertex(vAb), RED);
+DrawLine(ProjectVertex(vA), ProjectVertex(vAb), GREEN);
+DrawLine(ProjectVertex(vB), ProjectVertex(vBb), GREEN);
+DrawLine(ProjectVertex(vC), ProjectVertex(vCb), GREEN);
+DrawLine(ProjectVertex(vD), ProjectVertex(vDb), GREEN);
+
+UpdateCanvas();