小白的光线追踪之旅(二) | 三维球体的光线成像

上次是对于如何进行简单的二维颜色渲染做了一个初步入门，本次内容是对于光线追踪的第一次初步尝试。 在本次视频中，使用了glm开源图形库进行vector3的使用和简单成像。

关键程序如下:

// Renderer.h

#include "Walnut/Random.h"
#include <memory>
#include <glm/glm.hpp>

class Renderer
{
public:
	Renderer() = default;

	

	void OnResize(uint32_t width, uint32_t height);
	void Render();
	std::shared_ptr<Walnut::Image> GetFinalImage() const { return m_FinalImage; }
private:
	uint32_t PerPixel(glm::vec2 coord);
private:
	std::shared_ptr<Walnut::Image> m_FinalImage;
	uint32_t* m_ImageData = nullptr;
};

// Renderer.cpp

#include "Renderer.h"


void Renderer::OnResize(uint32_t width, uint32_t height)
{
	if (m_FinalImage)
	{
		// No resize necessary
		if (m_FinalImage->GetWidth() == width && m_FinalImage->GetHeight() == height)
		{
			return;
		}
		m_FinalImage->Resize(width, height);
	}
	else
	{
		m_FinalImage = std::make_shared<Walnut::Image>(width, height, Walnut::ImageFormat::RGBA);
	}
	
	delete[] m_ImageData;
	m_ImageData = new uint32_t[width * height];

}


void Renderer::Render()
{
	// render every pixel
	for (uint32_t y = 0; y < m_FinalImage->GetHeight(); ++y)
	{
		for (uint32_t x = 0; x < m_FinalImage->GetWidth(); ++x)
		{
			glm::vec2 coord = { (float)x / (float)m_FinalImage->GetWidth(), (float)y / (float)m_FinalImage->GetHeight() };
			coord = coord * 2.0f - 1.0f; // -1 -> 1
			m_ImageData[x + y * m_FinalImage->GetWidth()] = PerPixel(coord);

		}
	}
	m_FinalImage->SetData(m_ImageData);
}

uint32_t Renderer::PerPixel(glm::vec2 coord)
{
	uint8_t r = (uint8_t)(coord.x * 255.0f);
	uint8_t g = (uint8_t)(coord.y * 255.0f);

	glm::vec3 rayOrigin(0.0f, 0.0f, 2.0f);
	glm::vec3 rayDirection(coord.x, coord.y, -1.0f);
	float radius = 0.5f;
	// rayDirection = glm::normalize(rayDirection);

	// (bx^2 + by^2)t^2 + (2(axbx + ayby))t + (ax^2 + ay^2 - r^2) = 0
	// where
	// a = ray origin
	// b = ray direction
	// r = radius
	// t = hit distance
	
	//float a = coord.x * coord.x + coord.y * coord.y + coord.z * coord.z;
	float a = glm::dot(rayDirection, rayDirection);
	float b = 2.0f * glm::dot(rayOrigin, rayDirection);
	float c = glm::dot(rayOrigin, rayOrigin) - radius * radius;

	// Quaddratic forumula discriminant:
	// b^2 - 4ac

	float discriminant = b * b - 4.0f * a * c;

	if (discriminant >= 0.0f)
	{
		return 0xffff00ff;
	}
	return 0xff000000;
}

主程序调用如下：

	virtual void OnUIRender() override
	{
		ImGui::Begin("Setting");
		ImGui::Text("Last render: %.3fms", m_LastRenderTime);
		if (ImGui::Button("Render"))
		{
			Render();
		}
		ImGui::End();

		ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));
		ImGui::Begin("Viewport");

		m_ViewportWidth = ImGui::GetContentRegionAvail().x;
		m_ViewportHeight = ImGui::GetContentRegionAvail().y;

		auto image = m_Renderer.GetFinalImage();
		//ImGui::ShowDemoWindow();
		if(m_Renderer.GetFinalImage())
		    ImGui::Image(image->GetDescriptorSet(), { (float)image->GetWidth(), (float)image->GetHeight() },
				ImVec2(0, 1), ImVec2(1,0) );

		ImGui::End();
	    ImGui::PopStyleVar();

		Render();
	}
	void Render()
	{
		Timer timer;
		
		m_Renderer.OnResize(m_ViewportWidth, m_ViewportHeight);
		m_Renderer.Render();

		m_LastRenderTime = timer.ElapsedMillis();
	}

最终会显示一个粉色的球体:

虽然看起来就是画了一个二维圆，但是貌似是由光线追踪的数学原理成像得来的，等有时间再研究一下，等到下次再做总结吧。