GPU_batch: Add utility to create 2D shapes

Shapes are represented by compact byte array,
encoded by 'make_shape_2d_from_blend.py' in the tools repo.

source/blender/gpu/GPU_batch.h

@@ -43,6 +43,9 @@
 /* gpu_batch.c */
 void GWN_batch_program_set_builtin(Gwn_Batch *, GPUBuiltinShader);
 
+Gwn_Batch *GPU_batch_from_poly_2d_encoded(
+        const uchar *polys_flat, uint polys_flat_len, float min, float max);
+
 void gpu_batch_init(void);
 void gpu_batch_exit(void);
 

source/blender/gpu/intern/gpu_batch.c

@@ -29,7 +29,12 @@
  *  \ingroup gpu
  */
 
+#include "MEM_guardedalloc.h"
+
 #include "BLI_utildefines.h"
+#include "BLI_math.h"
+#include "BLI_polyfill2d.h"
+
 
 #include "GPU_batch.h"  /* own include */
 #include "gpu_shader_private.h"
@@ -44,6 +49,101 @@ void GWN_batch_program_set_builtin(Gwn_Batch *batch, GPUBuiltinShader shader_id)
 	GWN_batch_program_set(batch, shader->program, shader->interface);
 }
 
+/** \} */
+
+
+
+/* -------------------------------------------------------------------- */
+/** \name Batch Creation
+ * \{ */
+
+Gwn_Batch *GPU_batch_from_poly_2d_encoded(
+        const uchar *polys_flat, uint polys_flat_len, float min, float max)
+{
+	uchar (*polys)[2] = (void *)polys_flat;
+	uint polys_len = polys_flat_len / 2;
+
+	/* Over alloc in both cases */
+	float (*verts)[2] = MEM_mallocN(sizeof(*verts) * polys_len, __func__);
+	float (*verts_step)[2] = verts;
+	uint (*tris)[3] = MEM_mallocN(sizeof(*tris) * polys_len, __func__);
+	uint (*tris_step)[3] = tris;
+	const float range_uchar = (max - min) / 255.0f;
+
+	uint i_poly = 0;
+	uint i_vert = 0;
+	while (i_poly != polys_len) {
+		for (uint j = 0; j < 2; j++) {
+			verts[i_vert][j] = min + ((float)polys[i_poly][j] * range_uchar);
+		}
+		i_vert++;
+		i_poly++;
+		if (polys[i_poly - 1][0] == polys[i_poly][0] &&
+		    polys[i_poly - 1][1] == polys[i_poly][1])
+		{
+			const uint verts_len = (&verts[i_vert]) - verts_step;
+			BLI_assert(verts_len >= 3);
+			const uint tris_len = (verts_len - 2);
+			BLI_polyfill_calc(verts_step, verts_len, 0, tris_step);
+			/* offset indices */
+			if (verts_step != verts) {
+				uint *t = tris_step[0];
+				const uint offset = (verts_step - verts);
+				uint tot = tris_len * 3;
+				while (tot--) {
+					*t += offset;
+					t++;
+				}
+				BLI_assert(t == tris_step[tris_len]);
+			}
+			verts_step += verts_len;
+			tris_step += (verts_len - 2);
+			i_poly++;
+			/* ignore the duplicate point */
+		}
+	}
+
+	/* We have vertices and tris, make a batch from this. */
+	static Gwn_VertFormat format = {0};
+	static struct { uint pos; } attr_id;
+	if (format.attrib_ct == 0) {
+		attr_id.pos = GWN_vertformat_attr_add(&format, "pos", GWN_COMP_F32, 2, GWN_FETCH_FLOAT);
+	}
+
+	const uint verts_len = (verts_step - verts);
+	const uint tris_len = (tris_step - tris);
+	Gwn_VertBuf *vbo = GWN_vertbuf_create_with_format(&format);
+	GWN_vertbuf_data_alloc(vbo, verts_len);
+
+	Gwn_VertBufRaw pos_step;
+	GWN_vertbuf_attr_get_raw_data(vbo, attr_id.pos, &pos_step);
+
+	for (uint i = 0; i < verts_len; i++) {
+		copy_v2_v2(GWN_vertbuf_raw_step(&pos_step), verts[i]);
+	}
+
+	Gwn_IndexBufBuilder elb;
+	GWN_indexbuf_init(&elb, GWN_PRIM_TRIS, tris_len, verts_len);
+	for (uint i = 0; i < tris_len; i++) {
+		GWN_indexbuf_add_tri_verts(&elb, UNPACK3(tris[i]));
+	}
+	Gwn_IndexBuf *indexbuf = GWN_indexbuf_build(&elb);
+
+	MEM_freeN(tris);
+	MEM_freeN(verts);
+
+	return GWN_batch_create_ex(
+	        GWN_PRIM_TRIS, vbo,
+	        indexbuf,
+	        GWN_BATCH_OWNS_VBO | GWN_BATCH_OWNS_INDEX);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Init/Exit
+ * \{ */
+
 void gpu_batch_init(void)
 {
 	gpu_batch_presets_init();
@@ -55,4 +155,3 @@ void gpu_batch_exit(void)
 }
 
 /** \} */
-