veclavtlica
248 lines
8.5 KiB
C
248 lines
8.5 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 "fix.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 "zord.h"
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#include <stdint.h>
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#include <stdio.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.a[0]) + \
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((int64_t)a.a[m_n * 4 + 1] * b.a[1]) + \
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((int64_t)a.a[m_n * 4 + 2] * b.a[2]) + 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 render pixel space, reporting which
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* component lies outside of view. Bit test against those per component. This is
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* needed for 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 = 0;
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if (a.a[0] < -a.a[2] || a.a[0] > a.a[2])
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mask ^= COM_GEM_VERTEX_CLIPPED_X;
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if (a.a[1] < -a.a[2] || a.a[1] > a.a[2])
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mask ^= COM_GEM_VERTEX_CLIPPED_Y;
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// out->a[0] = com_fix_mul((com_fix_div(a.a[0], a.a[2]) + COM_FIX_FRACUNIT) >>
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// 1,
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// 640 * COM_FIX_FRACUNIT);
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// out->a[1] = com_fix_mul((com_fix_div(a.a[1], a.a[2]) + COM_FIX_FRACUNIT) >>
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// 1,
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// 480 * COM_FIX_FRACUNIT);
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out->a[0] =
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(com_fix_mul(com_fix_div(a.a[0], a.a[2]), 640 * COM_FIX_FRACUNIT) >>
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COM_FIX_FRACBITS) +
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320;
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out->a[1] =
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(com_fix_mul(com_fix_div(a.a[1], a.a[2]), 480 * COM_FIX_FRACUNIT) >>
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COM_FIX_FRACBITS) +
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240;
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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 *out) {
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int minX = com_vec_min(com_vec_from(v0.a[0], v1.a[0], v2.a[0]));
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int minY = com_vec_min(com_vec_from(v0.a[1], v1.a[1], v2.a[1]));
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int maxX = com_vec_max(com_vec_from(v0.a[0], v1.a[0], v2.a[0]));
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int maxY = com_vec_max(com_vec_from(v0.a[1], v1.a[1], v2.a[1]));
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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 = {.a = {x, y}};
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// Test the pixel center against all 3 edges
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com_vec_t ws = com_pnt_edge_weight(v0, v1, v2, p);
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// If the point is inside or on all edges, draw the pixel
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// (Assumes Counter Clockwise vertex ordering)
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if (ws.a[0] >= 0 && ws.a[1] >= 0 && ws.a[2] >= 0) {
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out[(y * 640 + x) * 4 + 0] = 125;
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out[(y * 640 + x) * 4 + 1] = 125;
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out[(y * 640 + x) * 4 + 2] = 125;
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}
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}
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}
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}
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/* TODO: Implement and compare:
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https://www.digipen.edu/sites/default/files/public/docs/theses/salem-haykal-digipen-master-of-science-in-computer-science-thesis-an-optimized-triangle-rasterizer.pdf
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Tile-based variant fares even worse than this implementation.
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*/
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static inline void
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com_gem_draw_triangle_textured_edge(com_pnt_t v0, com_pnt_t v1, com_pnt_t v2,
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uint8_t *out, com_pnt_t uv0, com_pnt_t uv1,
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com_pnt_t uv2, uint8_t *tex) {
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int minX = com_vec_min(com_vec_from(v0.a[0], v1.a[0], v2.a[0]));
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int minY = com_vec_min(com_vec_from(v0.a[1], v1.a[1], v2.a[1]));
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int maxX = com_vec_max(com_vec_from(v0.a[0], v1.a[0], v2.a[0]));
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int maxY = com_vec_max(com_vec_from(v0.a[1], v1.a[1], v2.a[1]));
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com_fix_t const area = com_pnt_area(v0, v1, v2);
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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 = {.a = {x, y}};
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// Test the pixel center against all 3 edges
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com_vec_t ws = com_pnt_edge_weight(v0, v1, v2, 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 (ws.a[0] >= 0 && ws.a[1] >= 0 && ws.a[2] >= 0) {
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// Barycentric weights
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ws = com_vec_div(ws, com_vec_scalar(area));
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// Affine interpolation of UVs.
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com_fix_t const u =
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(ws.a[0] * uv0.a[0] + ws.a[1] * uv1.a[0] + ws.a[2] * uv2.a[0]) >>
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COM_FIX_FRACBITS;
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com_fix_t const v =
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(ws.a[0] * uv0.a[1] + ws.a[1] * uv1.a[1] + ws.a[2] * uv2.a[1]) >>
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COM_FIX_FRACBITS;
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// Nearest-neighbor texture lookup, in [0..32) range.
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int32_t tx =
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(int32_t)((u + (COM_FIX_FRACUNIT / 2)) / (COM_FIX_FRACUNIT / 16));
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int32_t ty =
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(int32_t)((v + (COM_FIX_FRACUNIT / 2)) / (COM_FIX_FRACUNIT / 16));
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// uint32_t idx = com_zord_order(tx, ty);
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uint32_t idx = ty * 32 + tx;
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// uint32_t bidx = com_zord_order(x, y);
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uint32_t bidx = y * 640 + x;
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out[bidx * 4 + 0] = tex[idx * 3 + 0];
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out[bidx * 4 + 1] = tex[idx * 3 + 1];
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out[bidx * 4 + 2] = tex[idx * 3 + 2];
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}
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}
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}
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}
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static inline void draw_span(int32_t x_start_fp, int32_t x_end_fp, int y,
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uint8_t *out, uint8_t *tex) {
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int x1 = com_fix_int(
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x_start_fp + (1 << (COM_FIX_FRACBITS - 1))); // Rounding to nearest pixel
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int x2 = com_fix_int(x_end_fp + (1 << (COM_FIX_FRACBITS - 1)));
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if (x1 > x2) {
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int tmp = x1;
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x1 = x2;
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x2 = tmp;
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}
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for (int x = x1; x < x2; x++) {
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uint32_t idx = 0 * 32 + 0;
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uint32_t bidx = y * 640 + x;
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out[bidx * 4 + 0] = tex[idx * 3 + 0];
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out[bidx * 4 + 1] = tex[idx * 3 + 1];
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out[bidx * 4 + 2] = tex[idx * 3 + 2];
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}
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}
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static inline void
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com_gem_draw_triangle_textured_span(com_pnt_t v0, com_pnt_t v1, com_pnt_t v2,
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uint8_t *out, com_pnt_t uv0, com_pnt_t uv1,
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com_pnt_t uv2, uint8_t *tex) {
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// 1. Sort vertices by Y coordinate (v0.a[1] <= v1.a[1] <= v2.a[1])
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if (v0.a[1] > v1.a[1]) {
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com_pnt_t tmp = v0;
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v0 = v1;
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v1 = tmp;
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}
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if (v0.a[1] > v2.a[1]) {
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com_pnt_t tmp = v0;
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v0 = v2;
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v2 = tmp;
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}
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if (v1.a[1] > v2.a[1]) {
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com_pnt_t tmp = v1;
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v1 = v2;
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v2 = tmp;
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}
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// Guard against zero-height triangles
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if ((int)v0.a[1] == (int)v2.a[1])
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return;
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// 2. Compute overall inverse slopes (dX/dY) for all edges
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// Fixed-point division is performed using 64-bit integer casting to prevent
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// overflow
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com_fix_t dx02 = (v2.a[1] != v0.a[1])
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? (com_fix_t)((int64_t)(v2.a[0] - v0.a[0])
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<< COM_FIX_FRACBITS / (v2.a[1] - v0.a[1]))
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: 0;
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com_fix_t dx01 = (v1.a[1] != v0.a[1])
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? (com_fix_t)((int64_t)(v1.a[0] - v0.a[0])
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<< COM_FIX_FRACBITS / (v1.a[1] - v0.a[1]))
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: 0;
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com_fix_t dx12 = (v2.a[1] != v1.a[1])
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? (com_fix_t)((int64_t)(v2.a[0] - v1.a[0])
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<< COM_FIX_FRACBITS / (v2.a[1] - v1.a[1]))
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: 0;
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// Determine the scanline limits (pixel discrete boundaries)
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int y_start = com_fix_int(v0.a[1]);
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int y_mid = com_fix_int(v1.a[1]);
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int y_end = com_fix_int(v2.a[1]);
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// Initialize edge walkers starting at the top vertex (v0)
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com_fix_t edge1 = v0.a[0]; // Follows the long edge (v0 -> v2)
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com_fix_t edge2 = v0.a[0]; // Follows short edges (v0 -> v1, then v1 -> v2)
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// 3. Top Half Scan: Walk from top vertex to middle vertex breakpoint
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for (int y = y_start; y < y_mid; y++) {
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draw_span(edge1, edge2, y, out, tex);
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edge1 += dx02;
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edge2 += dx01;
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}
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// Adjust the short edge walker directly to the middle vertex position
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edge2 = v1.a[0];
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// 4. Bottom Half Scan: Walk from middle vertex to bottom vertex
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for (int y = y_mid; y < y_end; y++) {
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draw_span(edge1, edge2, y, out, tex);
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edge1 += dx02;
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edge2 += dx12;
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}
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}
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#endif
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