Add GL_LINE_STRIP_ADJACENCY support to Gawain

This primitive is used in geometry shaders like new grease pencil stroke shaders

intern/gawain/gawain/primitive.h

@@ -23,6 +23,7 @@ typedef enum {
 #endif
 
 	PRIM_LINE_STRIP = GL_LINE_STRIP,
+	PRIM_LINE_STRIP_ADJACENCY = GL_LINE_STRIP_ADJACENCY,
 	PRIM_LINE_LOOP = GL_LINE_LOOP, // GL has this, Vulkan does not
 	PRIM_TRIANGLE_STRIP = GL_TRIANGLE_STRIP,
 	PRIM_TRIANGLE_FAN = GL_TRIANGLE_FAN,

intern/gawain/src/immediate.c

@@ -160,6 +160,8 @@ static bool vertex_count_makes_sense_for_primitive(unsigned vertex_ct, Primitive
 		case PRIM_LINE_STRIP:
 		case PRIM_LINE_LOOP:
 			return vertex_ct >= 2;
+		case PRIM_LINE_STRIP_ADJACENCY:
+			return vertex_ct >= 4;
 		case PRIM_TRIANGLES:
 			return vertex_ct % 3 == 0;
 		case PRIM_TRIANGLE_STRIP: