veclavtlica
101 lines
3.4 KiB
C
101 lines
3.4 KiB
C
/*
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Geometry rendering.
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*/
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#ifndef COM_GEM_H
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#define COM_GEM_H
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#include "mat.h"
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#include "pnt.h"
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#include "vec.h"
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#include <stdint.h>
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/* Projects vertex position to a clip space via reordered row-major MVP matrix.
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It skips calculation of z depth component, as we assume to never use it.
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Instead, 3rd returned component is w value, for future projection.
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We must never render from inside geometry, as it will break no Z clipping
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assumption (see com_gem_clip_vis_project()).
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*/
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static inline com_vec_t com_gem_vec_project_clip(com_mat_t a, com_vec_t b) {
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com_vec_t result;
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#define CASE(m_c, m_n) \
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result.a[m_c] = (((int64_t)a.a[m_n * 4 + 0] * b.s.x) + \
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((int64_t)a.a[m_n * 4 + 1] * b.s.y) + \
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((int64_t)a.a[m_n * 4 + 2] * b.s.z) + a.a[m_n * 4 + 3]) >> \
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COM_FIX_FRACBITS;
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CASE(0, 0);
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CASE(1, 1);
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CASE(2, 3);
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#undef CASE
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return result;
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}
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/* TODO: Move to separate render-specific file. */
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/* TODO: If we clip test bounding volume of a model first we can skip
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* all clipping whatsoever, which might hold true more often, than the cost of
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* testing the volume. */
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/* TODO: It should be possible to have results in pixel position, not -1 to 1.
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*/
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#define COM_GEM_VERTEX_UNCLIPPED (0 << 0)
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#define COM_GEM_VERTEX_CLIPPED_X (1 << 0)
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#define COM_GEM_VERTEX_CLIPPED_Y (1 << 1)
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/* Attempt to project clip space vertex to NDC, reporting which component lies
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* outside of view. Bit test against those per component. This is needed for
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* determining new view-lying clipped triangles. */
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static inline uint8_t com_gem_clip_vis_project(com_vec_t a, com_pnt_t *out) {
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uint8_t mask;
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if (a.s.x < -a.s.z || a.s.x > a.s.z)
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mask ^= COM_GEM_VERTEX_CLIPPED_X;
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if (a.s.y < -a.s.z || a.s.y > a.s.z)
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mask ^= COM_GEM_VERTEX_CLIPPED_Y;
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out->a[0] = com_fix_div(a.a[0], a.a[2]) / 480 + 240;
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out->a[1] = com_fix_div(a.a[1], a.a[2]) / 640 + 320;
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return mask;
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}
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static inline void com_gem_draw_triangle(com_pnt_t v0, com_pnt_t v1,
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com_pnt_t v2, uint8_t *buffer) {
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// 1. Compute the bounding box of the triangle
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int minX = com_vec_min(com_vec_from(v0.s.x, v1.s.x, v2.s.x));
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int minY = com_vec_min(com_vec_from(v0.s.y, v1.s.y, v2.s.y));
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int maxX = com_vec_max(com_vec_from(v0.s.x, v1.s.x, v2.s.x));
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int maxY = com_vec_max(com_vec_from(v0.s.y, v1.s.y, v2.s.y));
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// 2. Clip the bounding box against screen dimensions to avoid out-of-bounds
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// errors
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// minX = CLAMP(minX, 0, 480 - 1);
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// minY = CLAMP(minY, 0, HEIGHT - 1);
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// maxX = CLAMP(maxX, 0, 480 - 1);
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// maxY = CLAMP(maxY, 0, HEIGHT - 1);
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// 3. Loop over all pixels inside the bounding box
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for (int y = minY; y <= maxY; y++) {
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for (int x = minX; x <= maxX; x++) {
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com_pnt_t p = {.s = {x, y}};
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// Test the pixel center against all 3 edges
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int w0 = com_pnt_edge_orient(v1, v2, p);
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int w1 = com_pnt_edge_orient(v2, v0, p);
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int w2 = com_pnt_edge_orient(v0, v1, p);
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// If the point is inside or on all edges, draw the pixel
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// (Assumes Clockwise vertex ordering)
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if (w0 >= 0 && w1 >= 0 && w2 >= 0) {
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printf("%i, %i\n", y, x);
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buffer[(y * 640 + x) * 4 + 0] = '#';
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buffer[(y * 640 + x) * 4 + 1] = '#';
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buffer[(y * 640 + x) * 4 + 2] = '#';
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buffer[(y * 640 + x) * 4 + 3] = '#';
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}
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}
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}
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}
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#endif
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