[gtk/wip/chergert/glproto] next: adjust vbo_offset when splitting draws

[Christian Hergert <chergert src gnome org>]

commit 9135ea200c8a9cfac8a5a5395a76b9bf45fd6fc8
Author: Christian Hergert <chergert redhat com>
Date:   Mon Feb 22 12:29:54 2021 -0800

    next: adjust vbo_offset when splitting draws
    
    In addition to splitting the draw, we also need to adjust the VBO offset
    because we batch added our verties above. We can calculate that from the
    previous batch offset+count quickly.

 gsk/next/gskglrenderjob.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)
---
diff --git a/gsk/next/gskglrenderjob.c b/gsk/next/gskglrenderjob.c
index cf51e265bc..ffae677f9a 100644
--- a/gsk/next/gskglrenderjob.c
+++ b/gsk/next/gskglrenderjob.c
@@ -2568,6 +2568,7 @@ gsk_gl_render_job_visit_text_node (GskGLRenderJob      *job,
   float x = offset->x + job->offset_x;
   float y = offset->y + job->offset_y;
   GskGLGlyphLibrary *library = job->driver->glyphs;
+  GskGLCommandBatch *batch;
   GskGLProgram *program;
   int x_position = 0;
   GskGLGlyphKey lookup;
@@ -2593,7 +2594,7 @@ gsk_gl_render_job_visit_text_node (GskGLRenderJob      *job,
   lookup.scale = (guint) (text_scale * 1024);
 
   gsk_gl_render_job_begin_draw (job, program);
-
+  batch = gsk_gl_command_queue_get_batch (job->command_queue);
   vertices = gsk_gl_command_queue_add_n_vertices (job->command_queue, num_glyphs);
 
   /* We use one quad per character */
@@ -2601,12 +2602,12 @@ gsk_gl_render_job_visit_text_node (GskGLRenderJob      *job,
     {
       const PangoGlyphInfo *gi = &glyphs[i];
       const GskGLGlyphValue *glyph;
+      guint base = used * GSK_GL_N_VERTICES;
       float glyph_x, glyph_y, glyph_x2, glyph_y2;
       float tx, ty, tx2, ty2;
       float cx;
       float cy;
       guint texture_id;
-      guint base;
 
       if (gi->glyph == PANGO_GLYPH_EMPTY)
         continue;
@@ -2619,16 +2620,26 @@ gsk_gl_render_job_visit_text_node (GskGLRenderJob      *job,
       if (!gsk_gl_glyph_library_lookup_or_add (library, &lookup, &glyph))
         goto next;
 
-      base = used * GSK_GL_N_VERTICES;
-
       texture_id = GSK_GL_TEXTURE_ATLAS_ENTRY_TEXTURE (glyph);
 
-      g_assert (texture_id > 0);
-
       if G_UNLIKELY (last_texture != texture_id)
         {
+          g_assert (texture_id > 0);
+
           if G_LIKELY (last_texture != 0)
-            gsk_gl_render_job_split_draw (job);
+            {
+              guint vbo_offset = batch->draw.vbo_offset + batch->draw.vbo_count;
+
+              /* Since we have batched added our VBO vertices to avoid repeated
+               * calls to the buffer, we need to manually tweak the vbo offset
+               * of the new batch as otherwise it will point at the end of our
+               * vbo array.
+               */
+              gsk_gl_render_job_split_draw (job);
+              batch = gsk_gl_command_queue_get_batch (job->command_queue);
+              batch->draw.vbo_offset = vbo_offset;
+            }
+
           gsk_gl_program_set_uniform_texture (program,
                                               UNIFORM_SHARED_SOURCE, 0,
                                               GL_TEXTURE_2D,
@@ -2677,7 +2688,7 @@ gsk_gl_render_job_visit_text_node (GskGLRenderJob      *job,
       vertices[base+5].uv[0] = tx2;
       vertices[base+5].uv[1] = ty;
 
-      gsk_gl_command_queue_get_batch (job->command_queue)->draw.vbo_count += GSK_GL_N_VERTICES;
+      batch->draw.vbo_count += GSK_GL_N_VERTICES;
       used++;
 
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