#include "R3DScrollFog.h"
#include "Graphics/Shader.h"

namespace New3D {

static const char *vertexShaderFog = R"glsl(

#version 410 core

void main(void)
{
	const vec4 vertices[] = vec4[](vec4(-1.0, -1.0, 0.0, 1.0),
									vec4(-1.0,  1.0, 0.0, 1.0),
									vec4( 1.0, -1.0, 0.0, 1.0),
									vec4( 1.0,  1.0, 0.0, 1.0));

	gl_Position = vertices[gl_VertexID % 4];
}

)glsl";

static const char *fragmentShaderFog = R"glsl(

#version 410 core

uniform float	fogAttenuation;
uniform float	fogAmbient;
uniform vec4	fogColour;
uniform vec3	spotFogColor;
uniform vec4	spotEllipse;

// Spotlight on fog
float	ellipse;
vec2	position, size;
vec3	lSpotFogColor;

// Scroll fog
float	lfogAttenuation;
vec3	lFogColor;
vec4	scrollFog;

// outputs
layout(location = 0) out vec4 out0;		// opaque
layout(location = 1) out vec4 out1;		// trans layer 1
layout(location = 2) out vec4 out2;		// trans layer 2

void WriteOutputs(vec4 colour)
{
	vec4 blank = vec4(0.0);
	
	if(colour.a < 1.0) {		// some transparency
		out0 = blank;
		out1 = colour;
		out2 = blank;
	}
	else {						// opaque
		out0 = colour;
		out1 = blank;
		out2 = blank;
	}
}

void main()
{
	// Scroll fog base color
	lFogColor = fogColour.rgb * fogAmbient;

	// Spotlight on fog (area) 
	position = spotEllipse.xy;
	size = spotEllipse.zw;
	ellipse = length((gl_FragCoord.xy - position) / size);
	ellipse = ellipse * ellipse;			// decay rate = square of distance from center
	ellipse = 1.0 - ellipse;				// invert
	ellipse = max(0.0, ellipse);			// clamp

	// Spotlight on fog (color)
	lSpotFogColor = mix(spotFogColor * ellipse * fogColour.rgb, vec3(0.0), fogAttenuation);

	// Scroll fog density
	scrollFog = vec4(lFogColor + lSpotFogColor, fogColour.a);

	// Final Color
	WriteOutputs(scrollFog);
}

)glsl";


R3DScrollFog::R3DScrollFog(const Util::Config::Node &config)
  : m_config(config),
	m_vao(0)
{
	m_shaderProgram		= 0;
	m_vertexShader		= 0;
	m_fragmentShader	= 0;

	AllocResources();

	glGenVertexArrays(1, &m_vao);
	glBindVertexArray(m_vao);
	// no states needed since we do it in the shader
	glBindVertexArray(0);
}

R3DScrollFog::~R3DScrollFog()
{
	DeallocResources();

	if (m_vao) {
		glDeleteVertexArrays(1, &m_vao);
		m_vao = 0;
	}
}

void R3DScrollFog::DrawScrollFog(float rgba[4], float attenuation, float ambient, float *spotRGB, float *spotEllipse)
{
	// some ogl states
	glDepthMask			(GL_FALSE);			// disable z writes
	glDisable			(GL_DEPTH_TEST);	// disable depth testing
	glEnable			(GL_BLEND);
	glBlendFunc			(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	glBindVertexArray	(m_vao);
	glUseProgram		(m_shaderProgram);
	glUniform4fv		(m_locFogColour, 1, rgba);
	glUniform1f			(m_locFogAttenuation, attenuation);
	glUniform1f			(m_locFogAmbient, ambient);
	glUniform3fv		(m_locSpotFogColor, 1, spotRGB);
	glUniform4fv		(m_locSpotEllipse, 1, spotEllipse);

	glDrawArrays		(GL_TRIANGLE_STRIP, 0, 4);

	glUseProgram		(0);
	glBindVertexArray	(0);

	glDisable			(GL_BLEND);
	glDepthMask			(GL_TRUE);
}

void R3DScrollFog::AllocResources()
{
	bool success = LoadShaderProgram(&m_shaderProgram, &m_vertexShader, &m_fragmentShader, m_config["VertexShaderFog"].ValueAs<std::string>(), m_config["FragmentShaderFog"].ValueAs<std::string>(), vertexShaderFog, fragmentShaderFog);

	m_locFogColour		= glGetUniformLocation(m_shaderProgram, "fogColour");
	m_locFogAttenuation	= glGetUniformLocation(m_shaderProgram, "fogAttenuation");
	m_locFogAmbient		= glGetUniformLocation(m_shaderProgram, "fogAmbient");
	m_locSpotFogColor	= glGetUniformLocation(m_shaderProgram, "spotFogColor");
	m_locSpotEllipse	= glGetUniformLocation(m_shaderProgram, "spotEllipse");
}

void R3DScrollFog::DeallocResources()
{
	if (m_shaderProgram) {
		DestroyShaderProgram(m_shaderProgram, m_vertexShader, m_fragmentShader);
	}

	m_shaderProgram		= 0;
	m_vertexShader		= 0;
	m_fragmentShader	= 0;
}

}