BLF: Optimize text rendering and caching

The current code allocates and transfers a lot of memory to the GPU,
but only a small portion of this memory is actually used.
In addition, the code calls many costly gl operations during the
caching process.

This commit significantly reduce the amount of memory by allocating
and transferring a flat array without pads to the GPU.
It also calls as little as possible the gl operations during the cache.

This code also simulate a billinear filter `GL_LINEAR` using a 1D texture.

**Average drawing time:**
|before:|0.00003184 sec
|now:|0.00001943 sec
|fac:|1.6385156675048407

**5 worst times:**
|before:|[0.001075, 0.001433, 0.002143, 0.002915, 0.003242]
|now:|[0.00094, 0.000993, 0.001502, 0.002284, 0.002328]

Differential Revision: https://developer.blender.org/D6886

1 files changed, 49 insertions, 4 deletions

diff --git a/source/blender/blenfont/intern/blf_font.c b/source/blender/blenfont/intern/blf_font.c
index 25ea0770f8b..f0afe184233 100644
--- a/source/blender/blenfont/intern/blf_font.c
+++ b/source/blender/blenfont/intern/blf_font.c
@@ -84,16 +84,19 @@ static void blf_batch_draw_init(void)
 {
   GPUVertFormat format = {0};
   g_batch.pos_loc = GPU_vertformat_attr_add(&format, "pos", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);
-  g_batch.tex_loc = GPU_vertformat_attr_add(&format, "tex", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);
   g_batch.col_loc = GPU_vertformat_attr_add(
       &format, "col", GPU_COMP_U8, 4, GPU_FETCH_INT_TO_FLOAT_UNIT);
+  g_batch.offset_loc = GPU_vertformat_attr_add(&format, "offset", GPU_COMP_I32, 1, GPU_FETCH_INT);
+  g_batch.glyph_size_loc = GPU_vertformat_attr_add(
+      &format, "glyph_size", GPU_COMP_I32, 2, GPU_FETCH_INT);
 
   g_batch.verts = GPU_vertbuf_create_with_format_ex(&format, GPU_USAGE_STREAM);
   GPU_vertbuf_data_alloc(g_batch.verts, BLF_BATCH_DRAW_LEN_MAX);
 
   GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.pos_loc, &g_batch.pos_step);
-  GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.tex_loc, &g_batch.tex_step);
   GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.col_loc, &g_batch.col_step);
+  GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.offset_loc, &g_batch.offset_step);
+  GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.glyph_size_loc, &g_batch.glyph_size_step);
   g_batch.glyph_len = 0;
 
   /* A dummy vbo containing 4 points, attribs are not used.  */
@@ -177,6 +180,46 @@ void blf_batch_draw_begin(FontBLF *font)
   }
 }
 
+static GPUTexture *blf_batch_cache_texture_load(void)
+{
+  GlyphCacheBLF *gc = g_batch.glyph_cache;
+  BLI_assert(gc);
+  BLI_assert(gc->bitmap_len > 0);
+
+  if (gc->bitmap_len > gc->bitmap_len_landed) {
+    const int tex_width = GPU_texture_width(gc->texture);
+
+    int bitmap_len_landed = gc->bitmap_len_landed;
+    int remain = gc->bitmap_len - bitmap_len_landed;
+    int offset_x = bitmap_len_landed % tex_width;
+    int offset_y = bitmap_len_landed / tex_width;
+
+    /* TODO(germano): Update more than one row in a single call. */
+    while (remain) {
+      int remain_row = tex_width - offset_x;
+      int width = remain > remain_row ? remain_row : remain;
+      GPU_texture_update_sub(gc->texture,
+                             GPU_DATA_UNSIGNED_BYTE,
+                             &gc->bitmap_result[bitmap_len_landed],
+                             offset_x,
+                             offset_y,
+                             0,
+                             width,
+                             1,
+                             0);
+
+      bitmap_len_landed += width;
+      remain -= width;
+      offset_x = 0;
+      offset_y += 1;
+    }
+
+    gc->bitmap_len_landed = bitmap_len_landed;
+  }
+
+  return gc->texture;
+}
+
 void blf_batch_draw(void)
 {
   if (g_batch.glyph_len == 0) {
@@ -190,7 +233,8 @@ void blf_batch_draw(void)
   /* We need to flush widget base first to ensure correct ordering. */
   UI_widgetbase_draw_cache_flush();
 
-  GPU_texture_bind(g_batch.tex_bind_state, 0);
+  GPUTexture *texture = blf_batch_cache_texture_load();
+  GPU_texture_bind(texture, 0);
   GPU_vertbuf_data_len_set(g_batch.verts, g_batch.glyph_len);
   GPU_vertbuf_use(g_batch.verts); /* send data */
 
@@ -202,8 +246,9 @@ void blf_batch_draw(void)
 
   /* restart to 1st vertex data pointers */
   GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.pos_loc, &g_batch.pos_step);
-  GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.tex_loc, &g_batch.tex_step);
   GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.col_loc, &g_batch.col_step);
+  GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.offset_loc, &g_batch.offset_step);
+  GPU_vertbuf_attr_get_raw_data(g_batch.verts, g_batch.glyph_size_loc, &g_batch.glyph_size_step);
   g_batch.glyph_len = 0;
 }