[gtk/wip/baedert/gl-rework: 101/127] gl renderer: Pass linear gradient stops to shaders directly

[Timm Bäder <baedert src gnome org>]

commit 68ed65ac9ca2d90c1f572142b34a9904f6ad8c91
Author: Timm Bäder <mail baedert org>
Date:   Tue Dec 17 18:11:45 2019 +0100

    gl renderer: Pass linear gradient stops to shaders directly
    
    No need to copy them into the render ops like this.

 gsk/gl/gskglrenderer.c                  | 34 +++++++--------------------------
 gsk/gl/gskglrenderopsprivate.h          |  1 -
 gsk/gl/opbuffer.h                       |  3 +--
 gsk/resources/glsl/linear_gradient.glsl | 29 ++++++++++++++++++++++------
 gsk/resources/glsl/preamble.vs.glsl     |  4 ++++
 5 files changed, 35 insertions(+), 36 deletions(-)
---
diff --git a/gsk/gl/gskglrenderer.c b/gsk/gl/gskglrenderer.c
index 68fcdf6ddb..59e434a41c 100644
--- a/gsk/gl/gskglrenderer.c
+++ b/gsk/gl/gskglrenderer.c
@@ -1137,23 +1137,10 @@ render_linear_gradient_node (GskGLRenderer   *self,
   const GskColorStop *stops = gsk_linear_gradient_node_peek_color_stops (node);
   const graphene_point_t *start = gsk_linear_gradient_node_peek_start (node);
   const graphene_point_t *end = gsk_linear_gradient_node_peek_end (node);
-  int i;
 
   ops_set_program (builder, &self->linear_gradient_program);
-
   op = ops_begin (builder, OP_CHANGE_LINEAR_GRADIENT);
-
-  for (i = 0; i < n_color_stops; i ++)
-    {
-      const GskColorStop *stop = stops + i;
-
-      op->color_stops[(i * 4) + 0] = stop->color.red;
-      op->color_stops[(i * 4) + 1] = stop->color.green;
-      op->color_stops[(i * 4) + 2] = stop->color.blue;
-      op->color_stops[(i * 4) + 3] = stop->color.alpha;
-      op->color_offsets[i] = stop->offset;
-    }
-
+  op->color_stops = stops;
   op->n_color_stops = n_color_stops;
   op->start_point.x = start->x + builder->dx;
   op->start_point.y = start->y + builder->dy;
@@ -2561,18 +2548,12 @@ apply_linear_gradient_op (const Program          *program,
                           const OpLinearGradient *op)
 {
   OP_PRINT (" -> Linear gradient");
-  glUniform1i (program->linear_gradient.num_color_stops_location,
-               op->n_color_stops);
-  glUniform4fv (program->linear_gradient.color_stops_location,
-                op->n_color_stops,
-                op->color_stops);
-  glUniform1fv (program->linear_gradient.color_offsets_location,
-                op->n_color_stops,
-                op->color_offsets);
-  glUniform2f (program->linear_gradient.start_point_location,
-               op->start_point.x, op->start_point.y);
-  glUniform2f (program->linear_gradient.end_point_location,
-               op->end_point.x, op->end_point.y);
+  glUniform1i (program->linear_gradient.num_color_stops_location, op->n_color_stops);
+  glUniform1fv (program->linear_gradient.color_stops_location,
+                op->n_color_stops * 5,
+                (float *)op->color_stops);
+  glUniform2f (program->linear_gradient.start_point_location, op->start_point.x, op->start_point.y);
+  glUniform2f (program->linear_gradient.end_point_location, op->end_point.x, op->end_point.y);
 }
 
 static inline void
@@ -2749,7 +2730,6 @@ gsk_gl_renderer_create_programs (GskGLRenderer  *self,
 
   /* linear gradient */
   INIT_PROGRAM_UNIFORM_LOCATION (linear_gradient, color_stops);
-  INIT_PROGRAM_UNIFORM_LOCATION (linear_gradient, color_offsets);
   INIT_PROGRAM_UNIFORM_LOCATION (linear_gradient, num_color_stops);
   INIT_PROGRAM_UNIFORM_LOCATION (linear_gradient, start_point);
   INIT_PROGRAM_UNIFORM_LOCATION (linear_gradient, end_point);
diff --git a/gsk/gl/gskglrenderopsprivate.h b/gsk/gl/gskglrenderopsprivate.h
index 216a457042..83554ab6f3 100644
--- a/gsk/gl/gskglrenderopsprivate.h
+++ b/gsk/gl/gskglrenderopsprivate.h
@@ -58,7 +58,6 @@ struct _Program
     struct {
       int num_color_stops_location;
       int color_stops_location;
-      int color_offsets_location;
       int start_point_location;
       int end_point_location;
     } linear_gradient;
diff --git a/gsk/gl/opbuffer.h b/gsk/gl/opbuffer.h
index e5198bb0b3..4c33babf97 100644
--- a/gsk/gl/opbuffer.h
+++ b/gsk/gl/opbuffer.h
@@ -109,8 +109,7 @@ typedef struct
 
 typedef struct
 {
-  float color_offsets[8];
-  float color_stops[4 * 8];
+  const GskColorStop *color_stops;
   graphene_point_t start_point;
   graphene_point_t end_point;
   int n_color_stops;
diff --git a/gsk/resources/glsl/linear_gradient.glsl b/gsk/resources/glsl/linear_gradient.glsl
index 0b5fefce83..6814eed53f 100644
--- a/gsk/resources/glsl/linear_gradient.glsl
+++ b/gsk/resources/glsl/linear_gradient.glsl
@@ -1,12 +1,16 @@
 // VERTEX_SHADER
 uniform vec2 u_start_point;
 uniform vec2 u_end_point;
+uniform float u_color_stops[8 * 5];
+uniform int u_num_color_stops;
 
 _OUT_ vec2 startPoint;
 _OUT_ vec2 endPoint;
 _OUT_ float maxDist;
 _OUT_ vec2 gradient;
 _OUT_ float gradientLength;
+_OUT_ vec4 color_stops[8];
+_OUT_ float color_offsets[8];
 
 void main() {
   gl_Position = u_projection * u_modelview * vec4(aPosition, 0.0, 1.0);
@@ -18,18 +22,31 @@ void main() {
   // Gradient direction
   gradient = endPoint - startPoint;
   gradientLength = length(gradient);
+
+  for (int i = 0; i < u_num_color_stops; i ++) {
+    color_offsets[i] = u_color_stops[(i * 5) + 0];
+    color_stops[i].r = u_color_stops[(i * 5) + 1];
+    color_stops[i].g = u_color_stops[(i * 5) + 2];
+    color_stops[i].b = u_color_stops[(i * 5) + 3];
+    color_stops[i].a = u_color_stops[(i * 5) + 4];
+  }
 }
 
 // FRAGMENT_SHADER:
-uniform vec4 u_color_stops[8];
-uniform float u_color_offsets[8];
+#ifdef GSK_LEGACY
 uniform int u_num_color_stops;
+#else
+uniform highp int u_num_color_stops; // Why? Because it works like this.
+#endif
 
 _IN_ vec2 startPoint;
 _IN_ vec2 endPoint;
 _IN_ float maxDist;
 _IN_ vec2 gradient;
 _IN_ float gradientLength;
+_IN_ vec4 color_stops[8];
+_IN_ float color_offsets[8];
+
 
 vec4 fragCoord() {
   vec4 f = gl_FragCoord;
@@ -49,11 +66,11 @@ void main() {
   // Offset of the current pixel
   float offset = length(proj) / maxDist;
 
-  vec4 color = u_color_stops[0];
+  vec4 color = color_stops[0];
   for (int i = 1; i < u_num_color_stops; i ++) {
-    if (offset >= u_color_offsets[i - 1])  {
-      float o = (offset - u_color_offsets[i - 1]) / (u_color_offsets[i] - u_color_offsets[i - 1]);
-      color = mix(u_color_stops[i - 1], u_color_stops[i], clamp(o, 0.0, 1.0));
+    if (offset >= color_offsets[i - 1])  {
+      float o = (offset - color_offsets[i - 1]) / (color_offsets[i] - color_offsets[i - 1]);
+      color = mix(color_stops[i - 1], color_stops[i], clamp(o, 0.0, 1.0));
     }
   }
 
diff --git a/gsk/resources/glsl/preamble.vs.glsl b/gsk/resources/glsl/preamble.vs.glsl
index 887482fee7..94c4f276a4 100644
--- a/gsk/resources/glsl/preamble.vs.glsl
+++ b/gsk/resources/glsl/preamble.vs.glsl
@@ -2,6 +2,10 @@ uniform mat4 u_projection;
 uniform mat4 u_modelview;
 uniform float u_alpha;
 
+#ifdef GSK_GLES
+precision highp float;
+#endif
+
 #if GSK_GLES
 #define _OUT_ varying
 #define _IN_ varying