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/*
* Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include "Sampler2D.h"
#include <LibGL/Tex/Texture2D.h>
#include <math.h>
namespace GL {
static constexpr float wrap_repeat(float value)
{
return value - floorf(value);
}
static constexpr float wrap_mirrored_repeat(float value)
{
float integer = floorf(value);
float frac = value - integer;
bool iseven = fmodf(integer, 2.0f) == 0.0f;
return iseven ? frac : 1 - frac;
}
static constexpr float wrap_clamp(float value)
{
return clamp(value, 0.0f, 1.0f);
}
static constexpr float wrap(float value, GLint mode)
{
switch (mode) {
case GL_REPEAT:
return wrap_repeat(value);
// FIXME: These clamp modes actually have slightly different behaviour
case GL_CLAMP:
case GL_CLAMP_TO_BORDER:
case GL_CLAMP_TO_EDGE:
return wrap_clamp(value);
case GL_MIRRORED_REPEAT:
return wrap_mirrored_repeat(value);
break;
default:
VERIFY_NOT_REACHED();
}
}
FloatVector4 Sampler2D::sample(FloatVector2 const& uv) const
{
// FIXME: Calculate the correct mipmap level here, need to receive uv derivatives for that
unsigned lod = 0;
MipMap const& mip = m_texture.mipmap(lod);
if (mip.width() < 1 || mip.height() < 1)
return { 1, 1, 1, 1 };
float x = wrap(uv.x(), m_wrap_t_mode);
float y = wrap(uv.y(), m_wrap_s_mode);
x *= mip.width() - 1;
y *= mip.height() - 1;
// Sampling implemented according to https://www.khronos.org/registry/OpenGL/specs/gl/glspec121.pdf Chapter 3.8
if (m_mag_filter == GL_NEAREST) {
return mip.texel(static_cast<unsigned>(x), static_cast<unsigned>(y));
} else if (m_mag_filter == GL_LINEAR) {
// FIXME: Implement different sampling points for wrap modes other than GL_REPEAT
x -= 0.5f;
y -= 0.5f;
unsigned i0 = static_cast<unsigned>(x) % mip.width();
unsigned j0 = static_cast<unsigned>(y) % mip.height();
unsigned i1 = (i0 + 1) % mip.width();
unsigned j1 = (j0 + 1) % mip.height();
auto t0 = mip.texel(i0, j0);
auto t1 = mip.texel(i1, j0);
auto t2 = mip.texel(i0, j1);
auto t3 = mip.texel(i1, j1);
float frac_x = x - floorf(x);
float frac_y = y - floorf(y);
float one_minus_frac_x = 1 - frac_x;
auto h1 = t0 * one_minus_frac_x + t1 * frac_x;
auto h2 = t2 * one_minus_frac_x + t3 * frac_x;
return h1 * (1 - frac_y) + h2 * frac_y;
} else {
VERIFY_NOT_REACHED();
}
}
}
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