Add 3D version of dashed line shader.

This is actually nearly same code as 2D version, maybe we can
deduplicate that later?

source/blender/gpu/CMakeLists.txt

@@ -150,6 +150,8 @@ data_to_c_simple(shaders/gpu_shader_3D_image_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_normal_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_flat_color_vert.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_3D_line_dashed_vert.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_3D_line_dashed_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_smooth_color_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_normal_smooth_color_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_smooth_color_frag.glsl SRC)

source/blender/gpu/GPU_shader.h

@@ -143,6 +143,7 @@ typedef enum GPUBuiltinShader {
 	GPU_SHADER_3D_POINT_VARYING_SIZE_VARYING_COLOR,
 	/* lines */
 	GPU_SHADER_2D_LINE_DASHED_COLOR,
+	GPU_SHADER_3D_LINE_DASHED_COLOR,
 	/* lamp drawing */
 	GPU_SHADER_3D_GROUNDPOINT,
 	GPU_SHADER_3D_GROUNDLINE,

source/blender/gpu/intern/gpu_shader.c

@@ -109,6 +109,8 @@ extern char datatoc_gpu_shader_2D_point_uniform_size_varying_color_outline_aa_ve
 
 extern char datatoc_gpu_shader_2D_line_dashed_vert_glsl[];
 extern char datatoc_gpu_shader_2D_line_dashed_frag_glsl[];
+extern char datatoc_gpu_shader_3D_line_dashed_vert_glsl[];
+extern char datatoc_gpu_shader_3D_line_dashed_frag_glsl[];
 
 extern char datatoc_gpu_shader_edges_front_back_persp_vert_glsl[];
 extern char datatoc_gpu_shader_edges_front_back_persp_geom_glsl[];
@@ -709,6 +711,8 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 
 		[GPU_SHADER_2D_LINE_DASHED_COLOR] = { datatoc_gpu_shader_2D_line_dashed_vert_glsl,
 		                                      datatoc_gpu_shader_2D_line_dashed_frag_glsl },
+	    [GPU_SHADER_3D_LINE_DASHED_COLOR] = { datatoc_gpu_shader_3D_line_dashed_vert_glsl,
+		                                      datatoc_gpu_shader_3D_line_dashed_frag_glsl },
 
 		[GPU_SHADER_3D_OBJECTSPACE_SIMPLE_LIGHTING_VARIYING_COLOR] =
 		    { datatoc_gpu_shader_instance_objectspace_variying_color_vert_glsl,

source/blender/gpu/shaders/gpu_shader_3D_line_dashed_frag.glsl

@@ -0,0 +1,24 @@
+
+/* Same code as 2D version actually, maybe we should deduplicate that? */
+
+#if __VERSION__ == 120
+  noperspective varying float distance_along_line;
+  #define fragColor gl_FragColor
+#else
+  noperspective in float distance_along_line;
+  out vec4 fragColor;
+#endif
+
+uniform float dash_width;
+uniform float dash_width_on;
+uniform vec4 color1;
+uniform vec4 color2;
+
+void main()
+{
+	if (mod(distance_along_line, dash_width) <= dash_width_on) {
+		fragColor = color1;
+	} else {
+		fragColor = color2;
+	}
+}

source/blender/gpu/shaders/gpu_shader_3D_line_dashed_vert.glsl

@@ -0,0 +1,32 @@
+
+/* Note: nearly the same code as for 2D version... Maybe we could deduplicate? */
+
+uniform mat4 ModelViewProjectionMatrix;
+uniform vec2 viewport_size;
+
+#if __VERSION__ == 120
+  attribute vec3 pos;
+  attribute vec3 line_origin; // = pos for one vertex of the line
+  noperspective varying float distance_along_line;
+#else
+  in vec3 pos;
+  in vec3 line_origin;
+  noperspective out float distance_along_line;
+#endif
+
+void main()
+{
+	gl_Position = ModelViewProjectionMatrix * vec4(pos, 1.0);
+
+	vec4 point = ModelViewProjectionMatrix * vec4(line_origin, 1.0);
+	vec2 ref_point = (point.xy / point.w) * 0.5 + 0.5;  // <- device coordinates in [0..1] range.
+	ref_point = ref_point * viewport_size;  // <- fragment coordinates.
+
+	vec2 curr_point = (gl_Position.xy / gl_Position.w) * 0.5 + 0.5;  // <- device coordinates in [0..1] range.
+	curr_point = curr_point * viewport_size;  // <- fragment coordinates.
+
+	distance_along_line = distance(ref_point, curr_point);
+
+	/* Note: we could also use similar approach as diag_stripes_frag, but this would give us dashed 'anchored'
+	 * to the screen, and not to one end of the line... */
+}