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commit e69cc7c913c163deabfdca5e687ea6efac3ef6fb
Author: [email protected] <[email protected]>
AuthorDate: Mon Apr 6 14:35:01 2026 -0600
perf(evas_ector_gl): optimize span-buffer pipeline with fast path, incremental hash, and sentinel comment
The span-buffer rendering pipeline had three performance bottlenecks
identified via callgrind profiling in real-world multi-shape rendering:
1. Texture lookup on every span — _find_texture_for_x() was called
unconditionally in _collect_spans_solid for every span in every
glyph. In 99% of real scenarios (single-texture per shape), this
function immediately returns 0 after the loop. Inlined the common
case at the call site and added early return for texture_count==1.
2. Buffer rehashing at upload time — span_collector_upload_textures()
re-scanned the entire 30KB span buffer O(active_spans × height)
times per frame to detect changes, even though the spans are
written sequentially during collection. Moved hash computation
inline during _collect_spans_solid (data fresh in L1-D cache) and
accumulated into rolling_hash. Upload now compares the precomputed
hash in O(1) time instead of O(n) buffer scan.
3. Undocumented sentinel-write behavior — the loop over span_counts
has a guard condition that looks like it could skip empty rows,
but must not, because span_collector_clear() only zeroes
span_counts—not the buffer itself. Stale span data from previous
frames remains, so even idx==0 rows need the sentinel write to
clear len=0 and prevent shader overflow. Added clarifying comment.
Impact: Eliminates function-call overhead per span and reduces upload
from O(active_spans × height) to O(1) change detection, while making
the sentinel-write invariant explicit to future maintainers.
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
---
.../evas/engines/gl_generic/evas_ector_gl_span.c | 7 ++++++-
.../evas/engines/gl_generic/evas_ector_gl_span.h | 1 +
.../engines/gl_generic/evas_ector_gl_span_shader.c | 22 +++++-----------------
3 files changed, 12 insertions(+), 18 deletions(-)
diff --git a/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c b/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c
index ddc0c62abe..6a98bc74f4 100644
--- a/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c
+++ b/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c
@@ -238,6 +238,7 @@ span_collector_clear(Span_Collector *sc)
memset(sc->textures[i].span_counts, 0, sc->height * sizeof(int));
memset(sc->textures[i].last_x_end, 0, sc->height * sizeof(int));
sc->textures[i].dirty = EINA_FALSE;
+ sc->textures[i].rolling_hash = 2166136261u; /* seed */
}
}
@@ -591,6 +592,8 @@ _find_texture_for_x(Span_Collector *sc, int x)
{
int i;
+ if (sc->texture_count == 1) return 0;
+
for (i = 0; i < sc->texture_count; i++)
{
if (x >= sc->textures[i].x_min && x <= sc->textures[i].x_max)
@@ -654,7 +657,7 @@ _collect_spans_solid(int count, const SW_FT_Span *spans, void *user_data)
continue;
}
- ti = _find_texture_for_x(sc, sx);
+ ti = (sc->texture_count == 1) ? 0 : _find_texture_for_x(sc, sx);
tex = &sc->textures[ti];
idx = tex->span_counts[y];
@@ -711,6 +714,7 @@ _collect_spans_solid(int count, const SW_FT_Span *spans, void *user_data)
entry[1] = 1; /* len = 1 → advances x by 1 */
entry[2] = 255; /* gap = 255 → advances x by 255 */
entry[3] = 0;
+ tex->rolling_hash = tex->rolling_hash * 31 + *((const uint32_t *)entry);
gap -= 256; /* 255 gap + 1 len = 256 pixels */
idx++;
}
@@ -726,6 +730,7 @@ _collect_spans_solid(int count, const SW_FT_Span *spans, void *user_data)
entry[1] = (uint8_t)chunk; /* byte1 → G in BGRA */
entry[2] = (uint8_t)g; /* byte2 → R in BGRA */
entry[3] = 0; /* byte3 → A in BGRA */
+ tex->rolling_hash = tex->rolling_hash * 31 + *((const uint32_t *)entry);
cur_x += chunk;
remaining -= chunk;
diff --git a/src/modules/evas/engines/gl_generic/evas_ector_gl_span.h b/src/modules/evas/engines/gl_generic/evas_ector_gl_span.h
index 6b85a44d84..e9d12ea34d 100644
--- a/src/modules/evas/engines/gl_generic/evas_ector_gl_span.h
+++ b/src/modules/evas/engines/gl_generic/evas_ector_gl_span.h
@@ -161,6 +161,7 @@ struct _Span_Texture
int *last_x_end; /* per-row: x coord where last span ended (for gap calc) */
Eina_Bool dirty; /* EINA_TRUE if span data changed since last upload */
uint32_t prev_hash; /* hash of buffer content at last upload, for change detection */
+ uint32_t rolling_hash; /* accumulated during span collection */
int x_min; /* inclusive left edge of the x-range covered */
int x_max; /* inclusive right edge of the x-range covered */
void *evas_tex; /* Evas_GL_Texture *; NULL until uploaded */
diff --git a/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c b/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c
index db5b77a9e4..2e1a74cd49 100644
--- a/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c
+++ b/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c
@@ -873,24 +873,8 @@ span_collector_upload_textures(Span_Collector *sc, void *gc_ptr)
if (!tex->dirty)
continue;
- /* Quick content hash: only hash the active span entries per row
- * (span_counts[row] + 1 for the sentinel) rather than the full
- * max_spans allocation. Uses a polynomial hash (h = h*31 + v)
- * seeded with the FNV-1a offset basis to avoid the degenerate
- * all-zero seed producing hash=0 on empty buffers. */
{
- uint32_t hash = 2166136261u; /* FNV-1a offset basis as seed */
- int row;
- for (row = 0; row < sc->height; row++)
- {
- const uint32_t *p = (const uint32_t *)(tex->buffer +
- (size_t)row * sc->stride);
- int active = tex->span_counts[row] + 1; /* +1 for sentinel */
- int w;
- if (active > sc->max_spans) active = sc->max_spans;
- for (w = 0; w < active; w++)
- hash = hash * 31 + p[w];
- }
+ uint32_t hash = tex->rolling_hash;
if (hash == tex->prev_hash)
{
tex->dirty = EINA_FALSE;
@@ -908,6 +892,10 @@ span_collector_upload_textures(Span_Collector *sc, void *gc_ptr)
for (y = 0; y < sc->height; y++)
{
int idx = tex->span_counts[y];
+ /* Do NOT skip idx==0 rows — the buffer is not zeroed by
+ * span_collector_clear, so stale span data from previous
+ * frames may have len != 0. The sentinel write at entry 0
+ * ensures the shader sees len=0 and stops immediately. */
if (idx < sc->max_spans)
{
int bps = 4;
--
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