opengl: batch drawing of polylines

To get polylines to draw in a batch it was necessary to refactor
the polyline code to work with GL_TRIANGLES instead of the previous
used GL_TRIANGLE_STRIP. For this and to make the code easier to
handle a new class was introduced: LineBuilder, which purpose is
to assemble vertices for a polyline (line ends, line joints).

In addition we need to know the line width, anti-aliasing (AA) per
vertex basis (in addition to color, normal and extrusion) so we
can draw many polylines with one draw call. This info is now
stored in Vertex struct which is used when drawing lines or
triangles (fills).

Uploading of vertices has also been changed, previously we
uploaded the vertices with the drawcall. a convention in Modern
OpenGL is however to use VBO (Vertex Buffer Object) for this.
With this we can upload the to the GPU vertices independently
and not upload them if this is not needed (which is currently
not used yet). A vector of Vertex structs is now uploaded to the
GPU using a VBO which is handeled with a new VertexBufferObject
class.

In addition to reduce the ammount of duplicated vertices, we use
a index vector (handled by IndexBufferObject class) where we only
define the indices of the vertex buffer which should be drawn.

Change-Id: I49dc9c6260b459f4f4ce3a5e4fa4c8ad05a7b878

1 files changed, 25 insertions, 7 deletions

diff --git a/vcl/opengl/combinedVertexShader.glsl b/vcl/opengl/combinedVertexShader.glsl
index 8c6a856cd7d6..3337a085db6f 100644
--- a/vcl/opengl/combinedVertexShader.glsl
+++ b/vcl/opengl/combinedVertexShader.glsl
@@ -14,6 +14,8 @@ attribute vec4 vertex_color_in;
 #endif
 
 varying float fade_factor; // fade factor for anti-aliasing
+varying float multiply;
+
 #ifdef USE_VERTEX_COLORS
 varying vec4 vertex_color;
 #endif
@@ -30,26 +32,42 @@ uniform int type;
 
 void main()
 {
-   vec4 final_position = vec4(position, 0.0, 1.0);
+   vec2 extrusion_vector = extrusion_vectors.xy;
+
+   float render_thickness = 0.0;
 
    if (type == TYPE_LINE)
    {
-      vec2 extrusion_vector = extrusion_vectors.xy;
       // miter factor to additionaly lenghten the distance of vertex (needed for miter)
       // if 1.0 - miter_factor has no effect
-      float miter_factor = 1.0f / abs(extrusion_vectors.z);
+      float miter_factor = 1.0 / abs(extrusion_vectors.z);
       // fade factor is always -1.0 or 1.0 -> we transport that info together with length
       fade_factor = sign(extrusion_vectors.z);
+#ifdef USE_VERTEX_COLORS
+      float the_feather = (1.0 + sign(extrusion_vectors.w)) / 4.0;
+      float the_line_width = abs(extrusion_vectors.w);
+#else
+      float the_feather = feather;
+      float the_line_width = line_width;
+#endif
+      render_thickness = (the_line_width * miter_factor + the_feather * 2.0 * miter_factor);
 
-      float rendered_thickness = (line_width + feather * 2.0) * miter_factor;
+      // Calculate the multiplier so we can transform the 0->1 fade factor
+      // to take feather and line width into account.
 
-      // lengthen the vertex in directon of the extrusion vector by line width.
-      final_position = vec4(position + (extrusion_vector * (rendered_thickness / 2.0) ), 0.0, 1.0);
+      float start = mix(0.0, (the_line_width / 2.0) - the_feather, the_feather * 2.0);
+      float end   = mix(1.0, (the_line_width / 2.0) + the_feather, the_feather * 2.0);
+
+      multiply = 1.0 / (1.0 - (start / end));
    }
 
+   // lengthen the vertex in directon of the extrusion vector by line width.
+   vec4 final_position = vec4(position + (extrusion_vector * (render_thickness / 2.0) ), 0.0, 1.0);
+
    gl_Position = mvp * final_position;
+
 #ifdef USE_VERTEX_COLORS
-   vertex_color = vertex_color_in;
+   vertex_color = vertex_color_in / 255.0;
 #endif
 }