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Optimize starfield rendering by replacing NanoVG paths with batched vertex-based rendering #7618

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Optimize starfield rendering by replacing NanoVG paths with batched vertex-based rendering #7618

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62 changes: 45 additions & 17 deletions code/starfield/starfield.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@
#include "cmdline/cmdline.h"
#include "debugconsole/console.h"
#include "graphics/matrix.h"
#include "graphics/paths/PathRenderer.h"
#include "graphics/render.h"
#include "hud/hud.h"
#include "hud/hudtarget.h"
#include "io/timer.h"
Expand Down Expand Up @@ -1774,12 +1774,16 @@ void stars_draw_stars()
tmp_num_stars = (Detail.num_stars * Num_stars) / MAX_DETAIL_VALUE;
CLAMP(tmp_num_stars, 0, Num_stars);

auto path = graphics::paths::PathRenderer::instance();

path->saveState();
path->resetState();

path->beginFrame();
// Streaks are batched into a single colored line list; issuing an
// individual NanoVG path per star costs enough CPU per stroke to dominate
// the frame in star-heavy scenes.
struct star_streak_vertex {
vec2d position;
vec4 color;
};
static SCP_vector<star_streak_vertex> star_verts;
star_verts.clear();
star_verts.reserve(static_cast<size_t>(tmp_num_stars) * 2);

for (i = 0; i < tmp_num_stars; i++) {
sp = &Stars[i];
Expand Down Expand Up @@ -1852,17 +1856,41 @@ void stars_draw_stars()
col.blue = (ubyte)((float)col.blue / powf(len, 1.0f / 2.2f));
col.alpha = (ubyte)((float)col.alpha / powf(len, 1.0f / 2.2f));
}
path->beginPath();

path->moveTo(p1.screen.xyw.x, p1.screen.xyw.y);
path->lineTo(p2.screen.xyw.x, p2.screen.xyw.y);

path->setStrokeColor(&col);
path->stroke();
star_streak_vertex vtx;
vtx.color.xyzw.x = col.red / 255.0f;
vtx.color.xyzw.y = col.green / 255.0f;
vtx.color.xyzw.z = col.blue / 255.0f;
vtx.color.xyzw.w = col.alpha / 255.0f;

vtx.position.x = p1.screen.xyw.x;
vtx.position.y = p1.screen.xyw.y;
star_verts.push_back(vtx);

vtx.position.x = p2.screen.xyw.x;
vtx.position.y = p2.screen.xyw.y;
star_verts.push_back(vtx);
}

if (!star_verts.empty()) {
material line_mat;
line_mat.set_blend_mode(ALPHA_BLEND_ALPHA_BLEND_ALPHA);
line_mat.set_depth_mode(ZBUFFER_TYPE_NONE);
line_mat.set_cull_mode(false);
line_mat.set_color(1.0f, 1.0f, 1.0f, 1.0f); // color comes from the vertices

vertex_layout layout;
layout.add_vertex_component(vertex_format_data::POSITION2, sizeof(star_streak_vertex),
offsetof(star_streak_vertex, position));
layout.add_vertex_component(vertex_format_data::COLOR4F, sizeof(star_streak_vertex),
offsetof(star_streak_vertex, color));

gr_render_primitives_2d_immediate(&line_mat,
PRIM_TYPE_LINES,
&layout,
static_cast<int>(star_verts.size()),
star_verts.data(),
star_verts.size() * sizeof(star_streak_vertex));
}
path->endFrame();

path->restoreState();
}

void stars_draw_motion_debris()
Expand Down
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