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src/display/primitives/skywall.c

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+/**
+ * Copyright (c) 2021 Dominic Masters
+ * 
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "skywall.h"
+
+void skywallInit(primitive_t *primitive) {
+  primitiveInit(primitive, SKYWALL_VERTICE_COUNT, SKYWALL_INDICE_COUNT);
+  
+  vertice_t vertices[SKYWALL_VERTICE_COUNT];
+  indice_t indices[SKYWALL_INDICE_COUNT];
+  int32_t n, i, j;
+  float x, z, p, r;
+  int32_t slices;
+
+  // For each slice. We iterate slices+1 to do the wrapping mentioned below.
+  for(i = 0; i < SKYWALL_SLICE_COUNT+1; i++) {
+    // Get the "percentage" of the current slice, slice 0 is 0, slice n is 1
+    p = (float)i/(float)SKYWALL_SLICE_COUNT;
+
+    // Because we we are to "seal the cylinder" we wrap around back to 0 on the
+    // last slice to have the last vertice meet the first.
+    if(SKYWALL_SLICE_COUNT == i) {
+      r = 0;
+    } else {
+      r = p * (float)M_PI * 2;// Convert % to radians
+    }
+
+    // Determine the X/Z for the given radian
+    x = SKYWALL_SIZE * (float)cos(r);
+    z = SKYWALL_SIZE * (float)sin(r);
+
+    // Get the start index for the ertices
+    n = i * SKYWALL_VERTICES_PER_SLICE;
+    vertices[n].x = x, vertices[n].y = -SKYWALL_SIZE, vertices[n].z = z;
+    vertices[n].u = p, vertices[n].v = 1;
+    vertices[n+1].x = x, vertices[n+1].y = SKYWALL_SIZE, vertices[n+1].z = z;
+    vertices[n+1].u = p, vertices[n+1].v = 0;
+
+    if(i == SKYWALL_SLICE_COUNT) continue;
+    j = i * SKYWALL_INDICES_PER_SLICE;
+    indices[j] = (indice_t)n;
+    indices[j+1] = (indice_t)n+1;
+    indices[j+2] = (indice_t)n+2;
+
+    indices[j+3] = (indice_t)n+3;
+    indices[j+4] = (indice_t)n+2;
+    indices[j+5] = (indice_t)n+1;
+  }
+
+  primitiveBufferVertices(primitive, 0, SKYWALL_VERTICE_COUNT, vertices);
+  primitiveBufferIndices(primitive, 0, SKYWALL_INDICE_COUNT, indices);
+}

src/display/primitives/skywall.h

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+// Copyright (c) 2021 Dominic Masters
+// 
+// This software is released under the MIT License.
+// https://opensource.org/licenses/MIT
+
+#pragma once
+#include <dawn/dawn.h>
+#include "../primitive.h"
+
+/** How many slices in each cylinder. */
+#define SKYWALL_SLICE_COUNT 20
+
+/** How many vertices per slice */
+#define SKYWALL_VERTICES_PER_SLICE 2
+
+/** How many indices per slice */
+#define SKYWALL_INDICES_PER_SLICE 6
+
+/** How many vertices in the cylinder, +1 to have the cylinder "wrap" */
+#define SKYWALL_VERTICE_COUNT (SKYWALL_SLICE_COUNT+1)*SKYWALL_VERTICES_PER_SLICE
+
+/** How many indices in the cylinder */
+#define SKYWALL_INDICE_COUNT SKYWALL_INDICES_PER_SLICE*SKYWALL_SLICE_COUNT
+
+/** How big the skywall cylinder is */
+#define SKYWALL_SIZE 100
+
+void skywallInit(primitive_t *primitive);