fixed to fix and some more

2026-09-13 20:57:34 +03:00
parent a1745f3a52
commit 4e1fa1ed1c
12 changed files with 356 additions and 276 deletions
@@ -0,0 +1,58 @@
+/*
+    Geometry rendering.
+*/
+
+#ifndef COM_GEM_H
+#define COM_GEM_H
+
+#include "mat.h"
+#include <stdint.h>
+
+/* Projects vertex position to a clip space via reordered row-major MVP matrix.
+   It skips calculation of z depth component, as we assume to never use it.
+   Instead, 3rd returned component is w value, for future projection.
+
+   We must never render from inside geometry, as it will break no Z clipping
+   assumption (see com_gem_clip_vis_project()).
+ */
+static inline com_vec_t com_gem_vec_project_clip(com_mat_t a, com_vec_t b) {
+  com_vec_t result;
+
+#define CASE(m_c, m_n)                                                         \
+  result.a[m_c] = (((int64_t)a.a[m_n * 4 + 0] * b.s.x) +                       \
+                   ((int64_t)a.a[m_n * 4 + 1] * b.s.y) +                       \
+                   ((int64_t)a.a[m_n * 4 + 2] * b.s.z) + a.a[m_n * 4 + 3]) >>  \
+                  COM_FIX_FRACBITS;
+
+  CASE(0, 0);
+  CASE(1, 1);
+  CASE(2, 3);
+
+#undef CASE
+
+  return result;
+}
+
+/* TODO: Move to separate render-specific file. */
+/* TODO: If we clip test bounding volume of a model first we can skip
+ * all clipping whatsoever, which might hold true more often, than the cost of
+ * testing the volume. */
+
+#define COM_GEM_VERTEX_UNCLIPPED (0 << 0)
+#define COM_GEM_VERTEX_CLIPPED_X (1 << 0)
+#define COM_GEM_VERTEX_CLIPPED_Y (1 << 1)
+/* Attempt to project clip space vertex to NDC, reporting which component lies
+ * outside of view. Bit test against those per component. This is needed for
+ * determining new view-lying clipped triangles. */
+static inline uint8_t com_gem_clip_vis_project(com_vec_t a, com_vec_t *out) {
+  uint8_t mask;
+  if (a.s.x < -a.s.z || a.s.x > a.s.z)
+    mask ^= COM_GEM_VERTEX_CLIPPED_X;
+  if (a.s.y < -a.s.z || a.s.y > a.s.z)
+    mask ^= COM_GEM_VERTEX_CLIPPED_Y;
+  out->a[0] = com_fix_div(a.a[0], a.a[2]);
+  out->a[1] = com_fix_div(a.a[1], a.a[2]);
+  return mask;
+}
+
+#endif