Helper.cpp

#include "Helper.h"
#include <SOIL/SOIL.h>
#include <iostream>

glm::vec3 convert(const btVector3& v)
{
	return glm::vec3(v.getX(), v.getY(), v.getZ());
}

btVector3 convert(glm::vec3 v)
{
	return btVector3(v.x, v.y, v.z);
}

btQuaternion convert(glm::quat q)
{
	return btQuaternion(q.x, q.y, q.z, q.w);
}

glm::quat convert(const btQuaternion& q)
{
	return glm::quat(q.getW(), q.getX(), q.getY(), q.getZ());
}

GLuint loadTexture(const char* fileName, bool alpha)
{
	int width, height;
	unsigned char* image;

	image = SOIL_load_image(fileName, &width, &height, 0, (alpha ? 
		SOIL_LOAD_RGBA : SOIL_LOAD_RGB));
	if (image == NULL) {
		std::cout << "Unable to open texture" << std::endl;
	}

	GLuint textureID;
	glGenTextures(1, &textureID);
	glBindTexture(GL_TEXTURE_2D, textureID);

	glTexImage2D(GL_TEXTURE_2D, 0, (alpha ? GL_RGBA : GL_RGB),
		width, height, 0, (alpha ? GL_RGBA : GL_RGB), GL_UNSIGNED_BYTE, image);
	
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);

	glBindTexture(GL_TEXTURE_2D, 0);

	SOIL_free_image_data(image);
	return textureID;
}

GLfloat lerp(GLfloat a, GLfloat b, GLfloat f)
{
	return a + f * (b - a);
}

//https://github.com/opengl-tutorials/ogl/blob/master/misc05_picking/misc05_picking_BulletPhysics.cpp
void ScreenPosToWorldRay(
	int mouseX, int mouseY,             // Mouse position, in pixels, from bottom-left corner of the window
	int screenWidth, int screenHeight,  // Window size, in pixels
	glm::mat4 ViewMatrix,               // Camera position and orientation
	glm::mat4 ProjectionMatrix,         // Camera parameters (ratio, field of view, near and far planes)
	glm::vec3& out_origin,              // Ouput : Origin of the ray. /!\ Starts at the near plane, so if you want the ray to start at the camera's position instead, ignore this.
	glm::vec3& out_direction            // Ouput : Direction, in world space, of the ray that goes "through" the mouse.
	)
{

	// The ray Start and End positions, in Normalized Device Coordinates (Have you read Tutorial 4 ?)
	glm::vec4 lRayStart_NDC(
		((float)mouseX / (float)screenWidth - 0.5f) * 2.0f, // [0,1024] -> [-1,1]
		((float)mouseY / (float)screenHeight - 0.5f) * 2.0f, // [0, 768] -> [-1,1]
		-1.0, // The near plane maps to Z=-1 in Normalized Device Coordinates
		1.0f
		);
	glm::vec4 lRayEnd_NDC(
		((float)mouseX / (float)screenWidth - 0.5f) * 2.0f,
		((float)mouseY / (float)screenHeight - 0.5f) * 2.0f,
		0.0,
		1.0f
		);


	// The Projection matrix goes from Camera Space to NDC.
	// So inverse(ProjectionMatrix) goes from NDC to Camera Space.
	glm::mat4 InverseProjectionMatrix = glm::inverse(ProjectionMatrix);

	// The View Matrix goes from World Space to Camera Space.
	// So inverse(ViewMatrix) goes from Camera Space to World Space.
	glm::mat4 InverseViewMatrix = glm::inverse(ViewMatrix);

	glm::vec4 lRayStart_camera = InverseProjectionMatrix * lRayStart_NDC;    
	lRayStart_camera /= lRayStart_camera.w;
	glm::vec4 lRayStart_world = InverseViewMatrix       * lRayStart_camera; 
	lRayStart_world /= lRayStart_world.w;
	glm::vec4 lRayEnd_camera = InverseProjectionMatrix * lRayEnd_NDC;      
	lRayEnd_camera /= lRayEnd_camera.w;
	glm::vec4 lRayEnd_world = InverseViewMatrix       * lRayEnd_camera;   
	lRayEnd_world /= lRayEnd_world.w;


	// Faster way (just one inverse)
	//glm::mat4 M = glm::inverse(ProjectionMatrix * ViewMatrix);
	//glm::vec4 lRayStart_world = M * lRayStart_NDC; 
	//lRayStart_world/=lRayStart_world.w;
	//glm::vec4 lRayEnd_world   = M * lRayEnd_NDC  ; 
	//lRayEnd_world  /=lRayEnd_world.w;


	glm::vec3 lRayDir_world(lRayEnd_world - lRayStart_world);
	lRayDir_world = glm::normalize(lRayDir_world);


	out_origin = glm::vec3(lRayStart_world);
	out_direction = glm::normalize(lRayDir_world);
}