// Gawain vertex format
//
// This code is part of the Gawain library, with modifications
// specific to integration with Blender.
//
// Copyright 2016 Mike Erwin
//
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of
// the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.

#include "gwn_vertex_format.h"
#include "gwn_vertex_format_private.h"
#include <stddef.h>
#include <string.h>

#define PACK_DEBUG 0

#if PACK_DEBUG
  #include <stdio.h>
#endif

void GWN_vertformat_clear(Gwn_VertFormat* format)
	{
#if TRUST_NO_ONE
	memset(format, 0, sizeof(Gwn_VertFormat));
#else
	format->attr_len = 0;
	format->packed = false;
	format->name_offset = 0;
	format->name_len = 0;

	for (unsigned i = 0; i < GWN_VERT_ATTR_MAX_LEN; i++)
		format->attribs[i].name_len = 0;
#endif
	}

void GWN_vertformat_copy(Gwn_VertFormat* dest, const Gwn_VertFormat* src)
	{
	// copy regular struct fields
	memcpy(dest, src, sizeof(Gwn_VertFormat));

	for (unsigned i = 0; i < dest->attr_len; i++)
		for (unsigned j = 0; j < dest->attribs[i].name_len; j++)
			dest->attribs[i].name[j] = (char *)dest + (src->attribs[i].name[j] - ((char *)src));
	}

static GLenum convert_comp_type_to_gl(Gwn_VertCompType type)
	{
	static const GLenum table[] = {
		[GWN_COMP_I8] = GL_BYTE,
		[GWN_COMP_U8] = GL_UNSIGNED_BYTE,
		[GWN_COMP_I16] = GL_SHORT,
		[GWN_COMP_U16] = GL_UNSIGNED_SHORT,
		[GWN_COMP_I32] = GL_INT,
		[GWN_COMP_U32] = GL_UNSIGNED_INT,

		[GWN_COMP_F32] = GL_FLOAT,

		[GWN_COMP_I10] = GL_INT_2_10_10_10_REV
		};
	return table[type];
	}

static unsigned comp_sz(Gwn_VertCompType type)
	{
#if TRUST_NO_ONE
	assert(type <= GWN_COMP_F32); // other types have irregular sizes (not bytes)
#endif

	const GLubyte sizes[] = {1,1,2,2,4,4,4};
	return sizes[type];
	}

static unsigned attrib_sz(const Gwn_VertAttr *a)
	{
	if (a->comp_type == GWN_COMP_I10)
		return 4; // always packed as 10_10_10_2

	return a->comp_len * comp_sz(a->comp_type);
	}

static unsigned attrib_align(const Gwn_VertAttr *a)
	{
	if (a->comp_type == GWN_COMP_I10)
		return 4; // always packed as 10_10_10_2

	unsigned c = comp_sz(a->comp_type);
	if (a->comp_len == 3 && c <= 2)
		return 4 * c; // AMD HW can't fetch these well, so pad it out (other vendors too?)
	else
		return c; // most fetches are ok if components are naturally aligned
	}

unsigned vertex_buffer_size(const Gwn_VertFormat* format, unsigned vertex_len)
	{
#if TRUST_NO_ONE
	assert(format->packed && format->stride > 0);
#endif

	return format->stride * vertex_len;
	}

static const char* copy_attrib_name(Gwn_VertFormat* format, const char* name)
	{
	// strncpy does 110% of what we need; let's do exactly 100%
	char* name_copy = format->names + format->name_offset;
	unsigned available = GWN_VERT_ATTR_NAMES_BUF_LEN - format->name_offset;
	bool terminated = false;

	for (unsigned i = 0; i < available; ++i)
		{
		const char c = name[i];
		name_copy[i] = c;
		if (c == '\0')
			{
			terminated = true;
			format->name_offset += (i + 1);
			break;
			}
		}

#if TRUST_NO_ONE
	assert(terminated);
	assert(format->name_offset <= GWN_VERT_ATTR_NAMES_BUF_LEN);
#else
	(void)terminated;
#endif

	return name_copy;
	}

unsigned GWN_vertformat_attr_add(Gwn_VertFormat* format, const char* name, Gwn_VertCompType comp_type, unsigned comp_len, Gwn_VertFetchMode fetch_mode)
	{
#if TRUST_NO_ONE
	assert(format->name_len < GWN_VERT_ATTR_MAX_LEN); // there's room for more
	assert(format->attr_len < GWN_VERT_ATTR_MAX_LEN); // there's room for more
	assert(!format->packed); // packed means frozen/locked
	assert((comp_len >= 1 && comp_len <= 4) || comp_len == 8 || comp_len == 12 || comp_len == 16);
	switch (comp_type)
		{
		case GWN_COMP_F32:
			// float type can only kept as float
			assert(fetch_mode == GWN_FETCH_FLOAT);
			break;
		case GWN_COMP_I10:
			// 10_10_10 format intended for normals (xyz) or colors (rgb)
			// extra component packed.w can be manually set to { -2, -1, 0, 1 }
			assert(comp_len == 3 || comp_len == 4);
			assert(fetch_mode == GWN_FETCH_INT_TO_FLOAT_UNIT); // not strictly required, may relax later
			break;
		default:
			// integer types can be kept as int or converted/normalized to float
			assert(fetch_mode != GWN_FETCH_FLOAT);
			// only support float matrices (see Batch_update_program_bindings)
			assert(comp_len != 8 && comp_len != 12 && comp_len != 16);
		}
#endif
	format->name_len++; // multiname support

	const unsigned attrib_id = format->attr_len++;
	Gwn_VertAttr* attrib = format->attribs + attrib_id;

	attrib->name[attrib->name_len++] = copy_attrib_name(format, name);
	attrib->comp_type = comp_type;
	attrib->gl_comp_type = convert_comp_type_to_gl(comp_type);
	attrib->comp_len = (comp_type == GWN_COMP_I10) ? 4 : comp_len; // system needs 10_10_10_2 to be 4 or BGRA
	attrib->sz = attrib_sz(attrib);
	attrib->offset = 0; // offsets & stride are calculated later (during pack)
	attrib->fetch_mode = fetch_mode;

	return attrib_id;
	}

void GWN_vertformat_alias_add(Gwn_VertFormat* format, const char* alias)
	{
	Gwn_VertAttr* attrib = format->attribs + (format->attr_len - 1);
#if TRUST_NO_ONE
	assert(format->name_len < GWN_VERT_ATTR_MAX_LEN); // there's room for more
	assert(attrib->name_len < GWN_VERT_ATTR_MAX_NAMES);
#endif
	format->name_len++; // multiname support
	attrib->name[attrib->name_len++] = copy_attrib_name(format, alias);
	}

unsigned padding(unsigned offset, unsigned alignment)
	{
	const unsigned mod = offset % alignment;
	return (mod == 0) ? 0 : (alignment - mod);
	}

#if PACK_DEBUG
static void show_pack(unsigned a_idx, unsigned sz, unsigned pad)
	{
	const char c = 'A' + a_idx;
	for (unsigned i = 0; i < pad; ++i)
		putchar('-');
	for (unsigned i = 0; i < sz; ++i)
		putchar(c);
	}
#endif

void VertexFormat_pack(Gwn_VertFormat* format)
	{
	// for now, attributes are packed in the order they were added,
	// making sure each attrib is naturally aligned (add padding where necessary)

	// later we can implement more efficient packing w/ reordering
	// (keep attrib ID order, adjust their offsets to reorder in buffer)

	// TODO:
	// realloc just enough to hold the final combo string. And just enough to
	// hold used attribs, not all 16.

	Gwn_VertAttr* a0 = format->attribs + 0;
	a0->offset = 0;
	unsigned offset = a0->sz;

#if PACK_DEBUG
	show_pack(0, a0->sz, 0);
#endif

	for (unsigned a_idx = 1; a_idx < format->attr_len; ++a_idx)
		{
		Gwn_VertAttr* a = format->attribs + a_idx;
		unsigned mid_padding = padding(offset, attrib_align(a));
		offset += mid_padding;
		a->offset = offset;
		offset += a->sz;

#if PACK_DEBUG
		show_pack(a_idx, a->sz, mid_padding);
#endif
		}

	unsigned end_padding = padding(offset, attrib_align(a0));

#if PACK_DEBUG
	show_pack(0, 0, end_padding);
	putchar('\n');
#endif

	format->stride = offset + end_padding;
	format->packed = true;
	}


// OpenGL ES packs in a different order as desktop GL but component conversion is the same.
// Of the code here, only struct Gwn_PackedNormal needs to change.

#define SIGNED_INT_10_MAX  511
#define SIGNED_INT_10_MIN -512

static int clampi(int x, int min_allowed, int max_allowed)
	{
#if TRUST_NO_ONE
	assert(min_allowed <= max_allowed);
#endif

	if (x < min_allowed)
		return min_allowed;
	else if (x > max_allowed)
		return max_allowed;
	else
		return x;
	}

static int quantize(float x)
	{
	int qx = x * 511.0f;
	return clampi(qx, SIGNED_INT_10_MIN, SIGNED_INT_10_MAX);
	}

static int convert_i16(short x)
	{
	// 16-bit signed --> 10-bit signed
	return x >> 6;
	// TODO: round?
	}

Gwn_PackedNormal GWN_normal_convert_i10_v3(const float data[3])
	{
	Gwn_PackedNormal n = { .x = quantize(data[0]), .y = quantize(data[1]), .z = quantize(data[2]) };
	return n;
	}

Gwn_PackedNormal GWN_normal_convert_i10_s3(const short data[3])
	{
	Gwn_PackedNormal n = { .x = convert_i16(data[0]), .y = convert_i16(data[1]), .z = convert_i16(data[2]) };
	return n;
	}