gl: Track the current uniform state for custom programs

This allows us to avoid updating uniforms if that is not necessary. This
in turn allows us to sometimes reuse the same draw op by just extending the
vertex array size we draw rather than doing a separate glDraw call.

For example, in the fishbowl demo, all the icons added at the same
time will have the same time and size, so we emit single draw calls
with 100s of triangles instead of 100s of draw calls with 2 triangles.

2 files changed, 27 insertions, 0 deletions

diff --git a/gsk/gl/gskglrenderops.c b/gsk/gl/gskglrenderops.c
index 1fc9d02810..63273db93d 100644
--- a/gsk/gl/gskglrenderops.c
+++ b/gsk/gl/gskglrenderops.c
@@ -640,7 +640,28 @@ ops_set_gl_shader_args (RenderOpBuilder       *builder,
                         float                  height,
                         const guchar          *uniform_data)
 {
+  ProgramState *current_program_state = get_current_program_state (builder);
   OpGLShader *op;
+  gsize args_size = gsk_gl_shader_get_args_size (shader);
+
+  if (current_program_state)
+    {
+      if (current_program_state->gl_shader.width == width &&
+          current_program_state->gl_shader.height == height &&
+          current_program_state->gl_shader.uniform_data_len == args_size &&
+          memcmp (current_program_state->gl_shader.uniform_data, uniform_data, args_size) == 0)
+        return;
+
+      current_program_state->gl_shader.width = width;
+      current_program_state->gl_shader.height = height;
+      if (args_size > sizeof (current_program_state->gl_shader.uniform_data))
+        current_program_state->gl_shader.uniform_data_len = 0;
+      else
+        {
+          current_program_state->gl_shader.uniform_data_len = args_size;
+          memcpy (current_program_state->gl_shader.uniform_data, uniform_data, args_size);
+        }
+    }
 
   op = ops_begin (builder, OP_CHANGE_GL_SHADER_ARGS);
   op->shader = shader;
diff --git a/gsk/gl/gskglrenderopsprivate.h b/gsk/gl/gskglrenderopsprivate.h
index 38b5756a9c..6f90a0c212 100644
--- a/gsk/gl/gskglrenderopsprivate.h
+++ b/gsk/gl/gskglrenderopsprivate.h
@@ -79,6 +79,12 @@ typedef struct
       float end;
       float radius[2]; /* h/v */
     } radial_gradient;
+    struct {
+      float width;
+      float height;
+      gint uniform_data_len;
+      guchar uniform_data[32];
+    } gl_shader;
   };
 } ProgramState;