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bgfx/examples/36-sky/sky.cpp

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/*
* Copyright 2017 Stanislav Pidhorskyi. All rights reserved.
* License: https://github.com/bkaradzic/bgfx/blob/master/LICENSE
*/
/*
* This example demonstrates:
* - Usage of Perez sky model [1] to render a dynamic sky.
* - Rendering a mesh with a lightmap, shading of which is driven by the same parameters as the sky.
*
* Typically, the sky is rendered using cubemaps or other environment maps.
* This approach can provide a high-quality sky, but the downside is that the
* image is static. To achieve daytime changes in sky appearance, there is a need
* in a dynamic model.
*
* Perez "An All-Weather Model for Sky Luminance Distribution" is a simple,
* but good enough model which is, in essence, a function that
* interpolates a sky color. As input, it requires several turbidity
* coefficients, a color at zenith and direction to the sun.
* Turbidity coefficients are taken from [2], which are computed using more
* complex physically based models. Color at zenith depends on daytime and can
* vary depending on many factors.
*
* In the code below, there are two tables that contain sky and sun luminance
* which were computed using code from [3]. Luminance in those tables
* represents actual scale of light energy that comes from sun compared to
* the sky.
*
* The sky is driven by luminance of the sky, while the material of the
* landscape is driven by both, the luminance of the sky and the sun. The
* lightening model is very simple and consists of two parts: directional
* light and hemisphere light. The first is used for the sun while the second
* is used for the sky. Additionally, the second part is modulated by a
* lightmap to achieve ambient occlusion effect.
*
* References
* ==========
*
* [1] R. Perez, R. Seals, and J. Michalsky."An All-Weather Model for Sky Luminance Distribution".
* Solar Energy, Volume 50, Number 3 (March 1993), pp. 235-245.
*
* [2] A. J. Preetham, Peter Shirley, and Brian Smits. "A Practical Analytic Model for Daylight",
* Proceedings of the 26th Annual Conference on Computer Graphics and Interactive Techniques,
* 1999, pp. 91-100.
* https://www.cs.utah.edu/~shirley/papers/sunsky/sunsky.pdf
*
* [3] E. Lengyel, Game Engine Gems, Volume One. Jones & Bartlett Learning, 2010. pp. 219 - 234
*
*/
#include "common.h"
#include "bgfx_utils.h"
#include "imgui/imgui.h"
#include "camera.h"
#include <map>
namespace
{
// Represents color. Color-space depends on context.
// In the code below, used to represent color in XYZ, and RGB color-space
typedef bx::Vec3 Color;
// HDTV rec. 709 matrix.
static constexpr float M_XYZ2RGB[] =
{
3.240479f, -0.969256f, 0.055648f,
-1.53715f, 1.875991f, -0.204043f,
-0.49853f, 0.041556f, 1.057311f,
};
// Converts color representation from CIE XYZ to RGB color-space.
Color xyzToRgb(const Color& xyz)
{
Color rgb(bx::init::None);
rgb.x = M_XYZ2RGB[0] * xyz.x + M_XYZ2RGB[3] * xyz.y + M_XYZ2RGB[6] * xyz.z;
rgb.y = M_XYZ2RGB[1] * xyz.x + M_XYZ2RGB[4] * xyz.y + M_XYZ2RGB[7] * xyz.z;
rgb.z = M_XYZ2RGB[2] * xyz.x + M_XYZ2RGB[5] * xyz.y + M_XYZ2RGB[8] * xyz.z;
return rgb;
};
// Precomputed luminance of sunlight in XYZ colorspace.
// Computed using code from Game Engine Gems, Volume One, chapter 15. Implementation based on Dr. Richard Bird model.
// This table is used for piecewise linear interpolation. Transitions from and to 0.0 at sunset and sunrise are highly inaccurate
static std::map<float, Color> sunLuminanceXYZTable =
{
{ 5.0f, { 0.000000f, 0.000000f, 0.000000f } },
{ 7.0f, { 12.703322f, 12.989393f, 9.100411f } },
{ 8.0f, { 13.202644f, 13.597814f, 11.524929f } },
{ 9.0f, { 13.192974f, 13.597458f, 12.264488f } },
{ 10.0f, { 13.132943f, 13.535914f, 12.560032f } },
{ 11.0f, { 13.088722f, 13.489535f, 12.692996f } },
{ 12.0f, { 13.067827f, 13.467483f, 12.745179f } },
{ 13.0f, { 13.069653f, 13.469413f, 12.740822f } },
{ 14.0f, { 13.094319f, 13.495428f, 12.678066f } },
{ 15.0f, { 13.142133f, 13.545483f, 12.526785f } },
{ 16.0f, { 13.201734f, 13.606017f, 12.188001f } },
{ 17.0f, { 13.182774f, 13.572725f, 11.311157f } },
{ 18.0f, { 12.448635f, 12.672520f, 8.267771f } },
{ 20.0f, { 0.000000f, 0.000000f, 0.000000f } },
};
// Precomputed luminance of sky in the zenith point in XYZ colorspace.
// Computed using code from Game Engine Gems, Volume One, chapter 15. Implementation based on Dr. Richard Bird model.
// This table is used for piecewise linear interpolation. Day/night transitions are highly inaccurate.
// The scale of luminance change in Day/night transitions is not preserved.
// Luminance at night was increased to eliminate need the of HDR render.
static std::map<float, Color> skyLuminanceXYZTable =
{
{ 0.0f, { 0.308f, 0.308f, 0.411f } },
{ 1.0f, { 0.308f, 0.308f, 0.410f } },
{ 2.0f, { 0.301f, 0.301f, 0.402f } },
{ 3.0f, { 0.287f, 0.287f, 0.382f } },
{ 4.0f, { 0.258f, 0.258f, 0.344f } },
{ 5.0f, { 0.258f, 0.258f, 0.344f } },
{ 7.0f, { 0.962851f, 1.000000f, 1.747835f } },
{ 8.0f, { 0.967787f, 1.000000f, 1.776762f } },
{ 9.0f, { 0.970173f, 1.000000f, 1.788413f } },
{ 10.0f, { 0.971431f, 1.000000f, 1.794102f } },
{ 11.0f, { 0.972099f, 1.000000f, 1.797096f } },
{ 12.0f, { 0.972385f, 1.000000f, 1.798389f } },
{ 13.0f, { 0.972361f, 1.000000f, 1.798278f } },
{ 14.0f, { 0.972020f, 1.000000f, 1.796740f } },
{ 15.0f, { 0.971275f, 1.000000f, 1.793407f } },
{ 16.0f, { 0.969885f, 1.000000f, 1.787078f } },
{ 17.0f, { 0.967216f, 1.000000f, 1.773758f } },
{ 18.0f, { 0.961668f, 1.000000f, 1.739891f } },
{ 20.0f, { 0.264f, 0.264f, 0.352f } },
{ 21.0f, { 0.264f, 0.264f, 0.352f } },
{ 22.0f, { 0.290f, 0.290f, 0.386f } },
{ 23.0f, { 0.303f, 0.303f, 0.404f } },
};
// Turbidity tables. Taken from:
// A. J. Preetham, P. Shirley, and B. Smits. A Practical Analytic Model for Daylight. SIGGRAPH '99
// Coefficients correspond to xyY colorspace.
static constexpr Color ABCDE[] =
{
{ -0.2592f, -0.2608f, -1.4630f },
{ 0.0008f, 0.0092f, 0.4275f },
{ 0.2125f, 0.2102f, 5.3251f },
{ -0.8989f, -1.6537f, -2.5771f },
{ 0.0452f, 0.0529f, 0.3703f },
};
static constexpr Color ABCDE_t[] =
{
{ -0.0193f, -0.0167f, 0.1787f },
{ -0.0665f, -0.0950f, -0.3554f },
{ -0.0004f, -0.0079f, -0.0227f },
{ -0.0641f, -0.0441f, 0.1206f },
{ -0.0033f, -0.0109f, -0.0670f },
};
// Performs piecewise linear interpolation of a Color parameter.
class DynamicValueController
{
typedef Color ValueType;
typedef std::map<float, ValueType> KeyMap;
public:
DynamicValueController()
{
}
~DynamicValueController()
{
}
void SetMap(const KeyMap& keymap)
{
m_keyMap = keymap;
}
ValueType GetValue(float time) const
{
typename KeyMap::const_iterator itUpper = m_keyMap.upper_bound(time + 1e-6f);
typename KeyMap::const_iterator itLower = itUpper;
--itLower;
if (itLower == m_keyMap.end())
{
return itUpper->second;
}
if (itUpper == m_keyMap.end())
{
return itLower->second;
}
float lowerTime = itLower->first;
const ValueType& lowerVal = itLower->second;
float upperTime = itUpper->first;
const ValueType& upperVal = itUpper->second;
if (lowerTime == upperTime)
{
return lowerVal;
}
return interpolate(lowerTime, lowerVal, upperTime, upperVal, time);
};
void Clear()
{
m_keyMap.clear();
};
private:
ValueType interpolate(float lowerTime, const ValueType& lowerVal, float upperTime, const ValueType& upperVal, float time) const
{
const float tt = (time - lowerTime) / (upperTime - lowerTime);
const ValueType result = bx::lerp(lowerVal, upperVal, tt);
return result;
};
KeyMap m_keyMap;
};
// Controls sun position according to time, month, and observer's latitude.
// Sun position computation based on Earth's orbital elements: https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
class SunController
{
public:
enum Month : int
{
January = 0,
February,
March,
April,
May,
June,
July,
August,
September,
October,
November,
December
};
SunController()
: m_northDir(1.0f, 0.0f, 0.0f)
, m_sunDir(0.0f, -1.0f, 0.0f)
, m_upDir(0.0f, 1.0f, 0.0f)
, m_latitude(50.0f)
, m_month(June)
, m_eclipticObliquity(bx::toRad(23.4f) )
, m_delta(0.0f)
{
}
void Update(float _time)
{
CalculateSunOrbit();
UpdateSunPosition(_time - 12.0f);
}
bx::Vec3 m_northDir;
bx::Vec3 m_sunDir;
bx::Vec3 m_upDir;
float m_latitude;
Month m_month;
private:
void CalculateSunOrbit()
{
const float day = 30.0f * float(m_month) + 15.0f;
float lambda = 280.46f + 0.9856474f * day;
lambda = bx::toRad(lambda);
m_delta = bx::asin(bx::sin(m_eclipticObliquity) * bx::sin(lambda) );
}
void UpdateSunPosition(float _hour)
{
const float latitude = bx::toRad(m_latitude);
const float hh = _hour * bx::kPi / 12.0f;
const float azimuth = bx::atan2(
bx::sin(hh)
, bx::cos(hh) * bx::sin(latitude) - bx::tan(m_delta) * bx::cos(latitude)
);
const float altitude = bx::asin(
bx::sin(latitude) * bx::sin(m_delta) + bx::cos(latitude) * bx::cos(m_delta) * bx::cos(hh)
);
const bx::Quaternion rot0 = bx::fromAxisAngle(m_upDir, -azimuth);
const bx::Vec3 dir = bx::mul(m_northDir, rot0);
const bx::Vec3 uxd = bx::cross(m_upDir, dir);
const bx::Quaternion rot1 = bx::fromAxisAngle(uxd, altitude);
m_sunDir = bx::mul(dir, rot1);
}
float m_eclipticObliquity;
float m_delta;
};
struct ScreenPosVertex
{
float m_x;
float m_y;
static void init()
{
ms_layout
.begin()
.add(bgfx::Attrib::Position, 2, bgfx::AttribType::Float)
.end();
}
static bgfx::VertexLayout ms_layout;
};
bgfx::VertexLayout ScreenPosVertex::ms_layout;
// Renders a screen-space grid of triangles.
// Because of performance reasons, and because sky color is smooth, sky color is computed in vertex shader.
// 32x32 is a reasonable size for the grid to have smooth enough colors.
struct ProceduralSky
{
void init(int verticalCount, int horizontalCount)
{
// Create vertex stream declaration.
ScreenPosVertex::init();
m_skyProgram = loadProgram("vs_sky", "fs_sky");
m_skyProgram_colorBandingFix = loadProgram("vs_sky", "fs_sky_color_banding_fix");
m_preventBanding = true;
bx::AllocatorI* allocator = entry::getAllocator();
ScreenPosVertex* vertices = (ScreenPosVertex*)BX_ALLOC(allocator
, verticalCount * horizontalCount * sizeof(ScreenPosVertex)
);
for (int i = 0; i < verticalCount; i++)
{
for (int j = 0; j < horizontalCount; j++)
{
ScreenPosVertex& v = vertices[i * verticalCount + j];
v.m_x = float(j) / (horizontalCount - 1) * 2.0f - 1.0f;
v.m_y = float(i) / (verticalCount - 1) * 2.0f - 1.0f;
}
}
uint16_t* indices = (uint16_t*)BX_ALLOC(allocator
, (verticalCount - 1) * (horizontalCount - 1) * 6 * sizeof(uint16_t)
);
int k = 0;
for (int i = 0; i < verticalCount - 1; i++)
{
for (int j = 0; j < horizontalCount - 1; j++)
{
indices[k++] = (uint16_t)(j + 0 + horizontalCount * (i + 0));
indices[k++] = (uint16_t)(j + 1 + horizontalCount * (i + 0));
indices[k++] = (uint16_t)(j + 0 + horizontalCount * (i + 1));
indices[k++] = (uint16_t)(j + 1 + horizontalCount * (i + 0));
indices[k++] = (uint16_t)(j + 1 + horizontalCount * (i + 1));
indices[k++] = (uint16_t)(j + 0 + horizontalCount * (i + 1));
}
}
m_vbh = bgfx::createVertexBuffer(bgfx::copy(vertices, sizeof(ScreenPosVertex) * verticalCount * horizontalCount), ScreenPosVertex::ms_layout);
m_ibh = bgfx::createIndexBuffer(bgfx::copy(indices, sizeof(uint16_t) * k));
BX_FREE(allocator, indices);
BX_FREE(allocator, vertices);
}
void shutdown()
{
bgfx::destroy(m_ibh);
bgfx::destroy(m_vbh);
bgfx::destroy(m_skyProgram);
bgfx::destroy(m_skyProgram_colorBandingFix);
}
void draw()
{
bgfx::setState(BGFX_STATE_WRITE_RGB | BGFX_STATE_DEPTH_TEST_EQUAL);
bgfx::setIndexBuffer(m_ibh);
bgfx::setVertexBuffer(0, m_vbh);
bgfx::submit(0, m_preventBanding ? m_skyProgram_colorBandingFix : m_skyProgram);
}
bgfx::VertexBufferHandle m_vbh;
bgfx::IndexBufferHandle m_ibh;
bgfx::ProgramHandle m_skyProgram;
bgfx::ProgramHandle m_skyProgram_colorBandingFix;
bool m_preventBanding;
};
class ExampleProceduralSky : public entry::AppI
{
public:
ExampleProceduralSky(const char* _name, const char* _description, const char* _url)
: entry::AppI(_name, _description, _url)
{
}
void init(int32_t _argc, const char* const* _argv, uint32_t _width, uint32_t _height) override
{
Args args(_argc, _argv);
m_width = _width;
m_height = _height;
m_debug = BGFX_DEBUG_NONE;
m_reset = BGFX_RESET_VSYNC;
bgfx::Init init;
init.type = args.m_type;
init.vendorId = args.m_pciId;
init.resolution.width = m_width;
init.resolution.height = m_height;
init.resolution.reset = m_reset;
bgfx::init(init);
// Enable m_debug text.
bgfx::setDebug(m_debug);
// Set view 0 clear state.
bgfx::setViewClear(0
, BGFX_CLEAR_COLOR | BGFX_CLEAR_DEPTH
, 0x000000ff
, 1.0f
, 0
);
m_sunLuminanceXYZ.SetMap(sunLuminanceXYZTable);
m_skyLuminanceXYZ.SetMap(skyLuminanceXYZTable);
m_mesh = meshLoad("meshes/test_scene.bin");
m_lightmapTexture = loadTexture("textures/lightmap.ktx");
// Imgui.
imguiCreate();
m_timeOffset = bx::getHPCounter();
m_time = 0.0f;
m_timeScale = 1.0f;
s_texLightmap = bgfx::createUniform("s_texLightmap", bgfx::UniformType::Sampler);
u_sunLuminance = bgfx::createUniform("u_sunLuminance", bgfx::UniformType::Vec4);
u_skyLuminanceXYZ = bgfx::createUniform("u_skyLuminanceXYZ", bgfx::UniformType::Vec4);
u_skyLuminance = bgfx::createUniform("u_skyLuminance", bgfx::UniformType::Vec4);
u_sunDirection = bgfx::createUniform("u_sunDirection", bgfx::UniformType::Vec4);
u_parameters = bgfx::createUniform("u_parameters", bgfx::UniformType::Vec4);
u_perezCoeff = bgfx::createUniform("u_perezCoeff", bgfx::UniformType::Vec4, 5);
m_landscapeProgram = loadProgram("vs_sky_landscape", "fs_sky_landscape");
m_sky.init(32, 32);
m_sun.Update(0);
cameraCreate();
cameraSetPosition({ 5.0f, 3.0, 0.0f });
cameraSetVerticalAngle(bx::kPi / 8.0f);
cameraSetHorizontalAngle(-bx::kPi / 3.0f);
m_turbidity = 2.15f;
}
virtual int shutdown() override
{
// Cleanup.
cameraDestroy();
imguiDestroy();
meshUnload(m_mesh);
m_sky.shutdown();
bgfx::destroy(s_texLightmap);
bgfx::destroy(u_sunLuminance);
bgfx::destroy(u_skyLuminanceXYZ);
bgfx::destroy(u_skyLuminance);
bgfx::destroy(u_sunDirection);
bgfx::destroy(u_parameters);
bgfx::destroy(u_perezCoeff);
bgfx::destroy(m_lightmapTexture);
bgfx::destroy(m_landscapeProgram);
bgfx::frame();
// Shutdown bgfx.
bgfx::shutdown();
return 0;
}
void imgui(float _width)
{
ImGui::Begin("ProceduralSky");
ImGui::SetWindowSize(ImVec2(_width, 200.0f) );
ImGui::SliderFloat("Time scale", &m_timeScale, 0.0f, 1.0f);
ImGui::SliderFloat("Time", &m_time, 0.0f, 24.0f);
ImGui::SliderFloat("Latitude", &m_sun.m_latitude, -90.0f, 90.0f);
ImGui::SliderFloat("Turbidity", &m_turbidity, 1.9f, 10.0f);
ImGui::Checkbox("Prevent color banding", &m_sky.m_preventBanding);
const char* items[] =
{
"January",
"February",
"March",
"April",
"May",
"June",
"July",
"August",
"September",
"October",
"November",
"December"
};
ImGui::Combo("Month", (int*)&m_sun.m_month, items, 12);
ImGui::End();
}
bool update() override
{
if (!entry::processEvents(m_width, m_height, m_debug, m_reset, &m_mouseState))
{
int64_t now = bx::getHPCounter();
static int64_t last = now;
const int64_t frameTime = now - last;
last = now;
const double freq = double(bx::getHPFrequency());
const float deltaTime = float(frameTime / freq);
m_time += m_timeScale * deltaTime;
m_time = bx::mod(m_time, 24.0f);
m_sun.Update(m_time);
imguiBeginFrame(m_mouseState.m_mx
, m_mouseState.m_my
, (m_mouseState.m_buttons[entry::MouseButton::Left] ? IMGUI_MBUT_LEFT : 0)
| (m_mouseState.m_buttons[entry::MouseButton::Right] ? IMGUI_MBUT_RIGHT : 0)
| (m_mouseState.m_buttons[entry::MouseButton::Middle] ? IMGUI_MBUT_MIDDLE : 0)
, m_mouseState.m_mz
, uint16_t(m_width)
, uint16_t(m_height)
);
showExampleDialog(this);
ImGui::SetNextWindowPos(
ImVec2(m_width - m_width / 5.0f - 10.0f, 10.0f)
, ImGuiCond_FirstUseEver
);
imgui(m_width / 5.0f - 10.0f);
imguiEndFrame();
// Update camera.
cameraUpdate(deltaTime, m_mouseState, ImGui::MouseOverArea() );
// Set view 0 default viewport.
bgfx::setViewRect(0, 0, 0, uint16_t(m_width), uint16_t(m_height));
float view[16];
cameraGetViewMtx(view);
float proj[16];
bx::mtxProj(proj, 60.0f, float(m_width) / float(m_height), 0.1f, 2000.0f, bgfx::getCaps()->homogeneousDepth);
bgfx::setViewTransform(0, view, proj);
Color sunLuminanceXYZ = m_sunLuminanceXYZ.GetValue(m_time);
Color sunLuminanceRGB = xyzToRgb(sunLuminanceXYZ);
Color skyLuminanceXYZ = m_skyLuminanceXYZ.GetValue(m_time);
Color skyLuminanceRGB = xyzToRgb(skyLuminanceXYZ);
bgfx::setUniform(u_sunLuminance, &sunLuminanceRGB.x);
bgfx::setUniform(u_skyLuminanceXYZ, &skyLuminanceXYZ.x);
bgfx::setUniform(u_skyLuminance, &skyLuminanceRGB.x);
bgfx::setUniform(u_sunDirection, &m_sun.m_sunDir.x);
float exposition[4] = { 0.02f, 3.0f, 0.1f, m_time };
bgfx::setUniform(u_parameters, exposition);
float perezCoeff[4 * 5];
computePerezCoeff(m_turbidity, perezCoeff);
bgfx::setUniform(u_perezCoeff, perezCoeff, 5);
bgfx::setTexture(0, s_texLightmap, m_lightmapTexture);
meshSubmit(m_mesh, 0, m_landscapeProgram, NULL);
m_sky.draw();
bgfx::frame();
return true;
}
return false;
}
void computePerezCoeff(float _turbidity, float* _outPerezCoeff)
{
const bx::Vec3 turbidity = { _turbidity, _turbidity, _turbidity };
for (uint32_t ii = 0; ii < 5; ++ii)
{
const bx::Vec3 tmp = bx::mad(ABCDE_t[ii], turbidity, ABCDE[ii]);
float* out = _outPerezCoeff + 4 * ii;
bx::store(out, tmp);
out[3] = 0.0f;
}
}
bgfx::ProgramHandle m_landscapeProgram;
bgfx::UniformHandle s_texLightmap;
bgfx::TextureHandle m_lightmapTexture;
bgfx::UniformHandle u_sunLuminance;
bgfx::UniformHandle u_skyLuminanceXYZ;
bgfx::UniformHandle u_skyLuminance;
bgfx::UniformHandle u_sunDirection;
bgfx::UniformHandle u_parameters;
bgfx::UniformHandle u_perezCoeff;
ProceduralSky m_sky;
SunController m_sun;
DynamicValueController m_sunLuminanceXYZ;
DynamicValueController m_skyLuminanceXYZ;
uint32_t m_width;
uint32_t m_height;
uint32_t m_debug;
uint32_t m_reset;
Mesh* m_mesh;
entry::MouseState m_mouseState;
float m_time;
float m_timeScale;
int64_t m_timeOffset;
float m_turbidity;
};
} // namespace
ENTRY_IMPLEMENT_MAIN(
ExampleProceduralSky
, "36-sky"
, "Perez dynamic sky model."
, "https://bkaradzic.github.io/bgfx/examples.html#sky"
);
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