PLYtoGX

PLYtoGX is a script capable of converting PLY 3D models into a corresponding set of libOGC GX calls. It can recognize triangularized meshes only and will operate on:

• Vertices
• Normals
• UV coords
• Vertex Colors (with or without alpha)

Note: Vertex coordinates, UV coordinates, and Normals are stored in float32 format. Vertex Colors are stored in RGB(A)_888(8) format.

Usage

GXConvert.py [-h] [-b B] [-s S] [-e E] FILE
  FILE        PLY file to process
options:
  -h, --help  show this help message and exit
  -b B        Output path for binary blob
  -s S        Output path for generated C file
  -e E        Output path for generated H file

The program will generate a binary .mdl file along with associated C and header files. The .mdl should be processed as part of your makefile in a similar way to other binary blobs. A small snippet like this in any libOGC makefile will handle it:

%.mdl.o	:	%.mdl
#---------------------------------------------------------------------------------
	@echo $(notdir $<)
	$(bin2o)

How it Works

PLYtoGLX packs model information into a flat binary blob <model>.mdl and configures the GX subsystem for Indirect Mode, allowing it to automatically index into the blob without CPU intervention. Additionally, the indices themselves are packed into a read-only array to further reduce code size.

The generated code stores color and UV information into their respective TEV channel 0s, although this can be changed by editing the resulting draw_<model>.c file.

Example Pyramid

Here's a simple pyramid

Which is represented by this ply file:

ply
format ascii 1.0
comment Created by Blender 3.2.0 - www.blender.org
element vertex 4
property float x
property float y
property float z
element face 4
property list uchar uint vertex_indices
end_header
-0.856242 0.856242 -0.977821
0.000000 0.000000 1.000000
1.137685 0.112052 -0.992718
-0.218203 -1.096980 -0.994841
3 0 1 2
3 2 1 3
3 3 1 0
3 2 3 0

After processing with GXConvert.py example/triangle.ply -b ~/prj/data -s ~/prj/src -e ~/prj/inc the following are generated:

PLYtoGX v1.0
Name:triangle Vertices:4 Faces:12
HasVtx:True HasNorm:False HasUv:False
HasColor:False HasColorAlpha:False
Packing binary model triangle.mdl ...
Generating C file draw_triangle.c ...
Generating H file draw_triangle.h ...

Generated Binary MDL File

 $ od -Ax -t f4x1 --endian big triangle.mdl 
000000       -0.856242        0.856242       -0.977821               0
	bf  5b  32  ad  3f  5b  32  ad  bf  7a  52  7a  00  00  00  00
000010               0               1        1.137685        0.112052
	00  00  00  00  3f  80  00  00  3f  91  9f  a9  3d  e5  7b  85
000020       -0.992718       -0.218203        -1.09698       -0.994841
	bf  7e  22  c4  be  5f  70  9b  bf  8c  69  d7  bf  7e  ad  e6

Generated C File

#include <ogc/gx.h>
#include "triangle_mdl.h"
static const u8 vtxArr[] = {0,1,2,2,1,3,3,1,0,2,3,0,};
void draw_triangle(void) {
	GX_ClearVtxDesc();
	GX_SetArray(GX_VA_POS, (void*)triangle_mdl+0, 12);
	GX_SetVtxDesc(GX_VA_POS, GX_INDEX8);
	GX_SetVtxAttrFmt(GX_VTXFMT0, GX_VA_POS, GX_POS_XYZ, GX_F32, 0);
	GX_Begin(GX_TRIANGLES, GX_VTXFMT0, 12);
	for(size_t i = 0; i<12; i++){
		GX_Position1x8(vtxArr[i]);
	}
	GX_End();
}

Using Textures (UNTESTED)

Texture data is not stored in PLY files and devkitPPC has a special, standardized mechanism for managing texture data as seen here. You will need to export your properly UV mapped texture into a standard 2D image format for conversion and linking. Take a look at this example project for more details on general texture use.

Before drawing the model, it is necessary to load the appropriate texture palette into memory. The simplest example (using the default GX_TEXMAP0 and GX_TEVSTAGE0) would be:

TEX_GetTexPalette(&tpl, "gxTextures.tpl");
TEX_GetTexObjFromPalette(tpl, &texObj, <MODEL_TEX_ID>);
GX_LoadTexObj(&texObj, GX_TEXMAP0);
GX_SetTevOp(GX_TEVSTAGE0, GX_MODULATE);
draw_<model>();