Add material, reflection and so on. Also use IntelliJ

.gitignore

@@ -1,4 +1,27 @@
-.idea/
-*.tga
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
 *.iml
+*.ipr
 out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Kotlin ###
+.kotlin
+
+
+### Mac OS ###
+.DS_Store
+
+
+test.tga

.idea/.gitignore

@@ -0,0 +1,3 @@
+# Default ignored files
+/shelf/
+/workspace.xml

.idea/.name

@@ -0,0 +1 @@
+Ray

.idea/codeStyles/Project.xml

@@ -0,0 +1,10 @@
+<component name="ProjectCodeStyleConfiguration">
+  <code_scheme name="Project" version="173">
+    <JetCodeStyleSettings>
+      <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
+    </JetCodeStyleSettings>
+    <codeStyleSettings language="kotlin">
+      <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
+    </codeStyleSettings>
+  </code_scheme>
+</component>

.idea/codeStyles/codeStyleConfig.xml

@@ -0,0 +1,5 @@
+<component name="ProjectCodeStyleConfiguration">
+  <state>
+    <option name="USE_PER_PROJECT_SETTINGS" value="true" />
+  </state>
+</component>

.idea/gradle.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
+  <component name="GradleSettings">
+    <option name="linkedExternalProjectsSettings">
+      <GradleProjectSettings>
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleJvm" value="17" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+          </set>
+        </option>
+      </GradleProjectSettings>
+    </option>
+  </component>
+</project>

.idea/kotlinc.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="KotlinJpsPluginSettings">
+    <option name="version" value="2.0.21" />
+  </component>
+</project>

.idea/misc.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="23" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>

build.gradle.kts

@@ -0,0 +1,18 @@
+plugins {
+    kotlin("jvm") version "2.0.21"
+}
+
+group = "org.example"
+version = "1.0-SNAPSHOT"
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation(kotlin("test"))
+}
+
+tasks.test {
+    useJUnitPlatform()
+}

gradle.properties

@@ -0,0 +1 @@
+kotlin.code.style=official

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Wed Nov 20 18:10:35 CET 2024
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.10-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle.kts

@@ -0,0 +1,2 @@
+rootProject.name = "Ray"
+

src/Ray.kt

@@ -1,130 +0,0 @@
-import java.io.File
-import java.lang.Float.max
-import kotlin.math.min
-import kotlin.math.pow
-import kotlin.math.sqrt
-
-data class Hit(val point: Point, val normal: Vector, val distance: Float, val color: MaterialColor)
-
-data class MaterialColor(val r: Float, val g: Float, val b: Float) {
-    fun toColor(): Color = Color(
-        (r * UByte.MAX_VALUE.toFloat()).toInt().toUByte(),
-        (g * UByte.MAX_VALUE.toFloat()).toInt().toUByte(),
-        (b * UByte.MAX_VALUE.toFloat()).toInt().toUByte()
-    )
-
-    operator fun times(rhs: MaterialColor) = MaterialColor(r * rhs.r, g * rhs.g, b * rhs.b)
-    operator fun plus(rhs: MaterialColor) = MaterialColor(r + rhs.r, g + rhs.g, b + rhs.b)
-}
-
-operator fun Float.times(rhs: MaterialColor) = MaterialColor(this * rhs.r, this * rhs.g, this * rhs.b)
-
-data class Ray(val origin: Point, val direction: Vector) {
-    fun at(t: Float) = origin + t * direction
-}
-
-interface Thing {
-    fun intersects(ray: Ray): Hit?
-}
-
-
-data class Plane(val point: Point, val normal: Vector, val color: MaterialColor) : Thing {
-    override fun intersects(ray: Ray): Hit? {
-        val bottom = dot(normal, ray.direction)
-        if (bottom == 0.0f) return null
-        val t = dot(normal, point - ray.origin) / bottom
-        if (t <= 0.0f) return null
-        return Hit(ray.at(t), normal, t, color)
-    }
-}
-
-data class Sphere(val center: Point, val radius: Float, val color: MaterialColor) : Thing {
-    override fun intersects(ray: Ray): Hit? {
-        val l = center - ray.origin
-        val tc = dot(l, ray.direction)
-        if (tc < 0f) return null
-
-        val d = l.squaredLength - tc * tc
-        val radiusSquared = radius * radius
-
-        if (d > radiusSquared) return null
-
-        val thc = sqrt(radiusSquared - d)
-
-        val t = min(tc - thc, tc + thc)
-
-        val hitPoint = ray.at(t)
-        return Hit(hitPoint, (hitPoint - center).normalized(), t, color)
-    }
-}
-
-fun dot(lhs: Vector, rhs: Vector): Float = lhs.x * rhs.x + lhs.y * rhs.y + lhs.z * rhs.z
-
-data class PointLight(val point: Point, val color: MaterialColor)
-
-data class Scene(val things: List<Thing>): Thing {
-    override fun intersects(ray: Ray): Hit? {
-        var closest: Hit? = null
-        for (thing in things) {
-            val hit = thing.intersects(ray)
-            if (hit != null && (closest == null || hit.distance < closest.distance)) {
-                closest = hit
-            }
-        }
-
-        return closest
-    }
-}
-
-fun main() {
-    val bmp = Bitmap(1000, 1000)
-    val origin = Point(500f, 500f, -500f)
-
-    val sphere = Sphere(Point(500f, 500f, 500f), radius = 500f, color = MaterialColor(0f, 1.0f, 0f))
-    val plane = Plane(
-        Point(0f, -1000f, 0f),
-        normal = Vector(0f, 1f, 0f),
-        color = MaterialColor(0.5f, 0.5f, 0.5f)
-    )
-
-    val leftPlane = Plane(
-        Point(-1000f, 0f, 0f),
-        Vector(1f, 0f, 0f),
-        color = MaterialColor(0.9f, 0.9f, 0.5f)
-    )
-
-    val scene = Scene(listOf(sphere, plane, leftPlane))
-
-    val ambient = MaterialColor(0.1f, 0.1f, 0.1f)
-
-    val light = PointLight(Point(1000f, 1000f, -500f), color = MaterialColor(0.5f, 0.5f, 0.5f))
-    val specular = 100f
-
-    for (y in 0 until bmp.height) {
-        for (x in 0 until bmp.width) {
-            val point = Point(x.toFloat(), y.toFloat(), 0f)
-            val ray = origin.rayTo(point)
-
-            val hit = scene.intersects(ray)
-            if (hit != null) {
-                var color = hit.color * ambient
-
-                val rayToLight = (hit.point + 0.0001f * hit.normal).rayTo(light.point)
-                if (scene.intersects(rayToLight) == null) {
-
-                    val lambert = max(0f, dot(hit.normal, rayToLight.direction))
-                    color += lambert * light.color
-
-                    val h = (-ray.direction + rayToLight.direction).normalized()
-
-                    val intensity = dot(hit.normal, h).pow(specular)
-
-                    color += intensity * MaterialColor(0.3f, 0f, 0f)
-                }
-
-                bmp.setPixel(x, y, color.toColor())
-            }
-        }
-    }
-    File("test.tga").writeBitmap(bmp)
-}

src/main/kotlin/Ray.kt

@@ -0,0 +1,190 @@
+import java.io.File
+import java.lang.Float.max
+import kotlin.math.min
+import kotlin.math.pow
+import kotlin.math.sqrt
+
+data class Hit(val point: Point, val normal: Vector, val distance: Float, val material: Material)
+
+data class MaterialColor(val r: Float, val g: Float, val b: Float) {
+    fun toColor(): Color = Color(
+        (r * UByte.MAX_VALUE.toFloat()).toInt().toUByte(),
+        (g * UByte.MAX_VALUE.toFloat()).toInt().toUByte(),
+        (b * UByte.MAX_VALUE.toFloat()).toInt().toUByte()
+    )
+
+    operator fun times(rhs: MaterialColor) = MaterialColor(r * rhs.r, g * rhs.g, b * rhs.b)
+    operator fun plus(rhs: MaterialColor) = MaterialColor(r + rhs.r, g + rhs.g, b + rhs.b)
+
+    companion object {
+        val Black: MaterialColor = MaterialColor(0f, 0f, 0f)
+    }
+}
+
+operator fun Float.times(rhs: MaterialColor) = MaterialColor(this * rhs.r, this * rhs.g, this * rhs.b)
+
+data class Ray(val origin: Point, val direction: Vector) {
+    fun at(t: Float) = origin + t * direction
+}
+
+interface Thing {
+    fun intersects(ray: Ray): Hit?
+}
+
+interface Material {
+    fun shade(ray: Ray, hit: Hit, scene: Scene): MaterialColor
+}
+
+data class WhateverMaterial(val color: MaterialColor,
+                            val ambient: MaterialColor = MaterialColor(0.1f, 0.1f, 0.1f),
+                            val specular: Float = 100f
+): Material {
+    override fun shade(ray: Ray, hit: Hit, scene: Scene): MaterialColor {
+        var color = this.color * ambient
+        val light = scene.light
+        val rayToLight = (hit.point + 0.0001f * hit.normal).rayTo(light.point)
+        if (scene.intersects(rayToLight) == null) {
+
+            val lambert = max(0f, dot(hit.normal, rayToLight.direction))
+            color += lambert * light.color
+
+            val h = (-ray.direction + rayToLight.direction).normalized()
+
+            val intensity = dot(hit.normal, h).pow(specular)
+
+            color += intensity * MaterialColor(0.3f, 0f, 0f)
+        }
+
+        return color
+    }
+}
+
+data class ReflectiveMaterial(
+                            val reflectivity: Float,
+                            val color: MaterialColor,
+                            val ambient: MaterialColor = MaterialColor(0.1f, 0.1f, 0.1f),
+                            val specular: Float = 10f
+): Material {
+    override fun shade(ray: Ray, hit: Hit, scene: Scene): MaterialColor {
+        var color = this.color * ambient
+        val light = scene.light
+        val offsetPoint = hit.point + 0.0001f * hit.normal
+        val rayToLight = offsetPoint.rayTo(light.point)
+        if (scene.intersects(rayToLight) == null) {
+
+            val lambert = max(0f, dot(hit.normal, rayToLight.direction))
+            color += lambert * light.color
+
+            val h = (-ray.direction + rayToLight.direction).normalized()
+
+            val intensity = (hit.normal dot h).pow(specular)
+
+            color += intensity * MaterialColor(0.3f, 0f, 0f)
+        }
+
+        val reflectionDirection = ray.direction - 2 * (ray.direction dot hit.normal) * hit.normal
+        val reflectedColor = scene.colorForRay(Ray(offsetPoint, reflectionDirection)) ?: MaterialColor.Black
+
+        return  (1.0f - reflectivity) * color + reflectivity * reflectedColor
+    }
+}
+
+
+data class Plane(val point: Point, val normal: Vector, val material: Material) : Thing {
+    override fun intersects(ray: Ray): Hit? {
+        val bottom = dot(normal, ray.direction)
+        if (bottom == 0.0f) return null
+        val t = dot(normal, point - ray.origin) / bottom
+        if (t <= 0.0f) return null
+        return Hit(ray.at(t), normal, t, material)
+    }
+}
+
+data class Sphere(val center: Point, val radius: Float, val material: Material) : Thing {
+    override fun intersects(ray: Ray): Hit? {
+        val l = center - ray.origin
+        val tc = dot(l, ray.direction)
+        if (tc < 0f) return null
+
+        val d = l.squaredLength - tc * tc
+        val radiusSquared = radius * radius
+
+        if (d > radiusSquared) return null
+
+        val thc = sqrt(radiusSquared - d)
+
+        val t = min(tc - thc, tc + thc)
+
+        val hitPoint = ray.at(t)
+        return Hit(hitPoint, (hitPoint - center).normalized(), t, material)
+    }
+}
+
+fun dot(lhs: Vector, rhs: Vector): Float = lhs.x * rhs.x + lhs.y * rhs.y + lhs.z * rhs.z
+
+data class PointLight(val point: Point, val color: MaterialColor)
+
+data class Scene(val things: List<Thing>, val light: PointLight): Thing {
+    override fun intersects(ray: Ray): Hit? {
+        var closest: Hit? = null
+        for (thing in things) {
+            val hit = thing.intersects(ray)
+            if (hit != null && (closest == null || hit.distance < closest.distance)) {
+                closest = hit
+            }
+        }
+
+        return closest
+    }
+
+    fun colorForRay(ray: Ray): MaterialColor? {
+        val hit = intersects(ray)
+        if (hit != null) {
+            return hit.material.shade(ray, hit, this)
+        }
+        return null
+    }
+}
+
+fun main() {
+    val bmp = Bitmap(1000, 1000)
+    val origin = Point(500f, 500f, -500f)
+
+    val sphere = Sphere(Point(500f, 500f, 500f), radius = 500f, material = ReflectiveMaterial(reflectivity = 0.2f, MaterialColor(0f, 1.0f, 0f)))
+    val sphere2 = Sphere(Point(0f, 500f, 50f), radius = 50f, material = ReflectiveMaterial(reflectivity = 0.2f, MaterialColor(1.0f, 0.0f, 0.1f)))
+
+    val plane = Plane(
+        Point(0f, -1000f, 0f),
+        normal = Vector(0f, 1f, 0f),
+        material = WhateverMaterial(MaterialColor(1f, 0.0f, 0.0f))
+    )
+
+    val leftPlane = Plane(
+        Point(-1000f, 0f, 0f),
+        Vector(1f, 0f, 0f),
+        material = WhateverMaterial(MaterialColor(0.0f, 1f, 0.0f))
+    )
+
+    val light = PointLight(Point(1000f, 1000f, -500f), color = 0.2f * MaterialColor(0.9f, 0.9f, 0.9f))
+
+    val scene = Scene(listOf(
+        sphere,
+        sphere2,
+        plane,
+        leftPlane
+    ), light = light)
+
+
+    for (y in 0 until bmp.height) {
+        for (x in 0 until bmp.width) {
+            val point = Point(x.toFloat(), y.toFloat(), 0f)
+            val ray = origin.rayTo(point)
+
+            val color = scene.colorForRay(ray)
+            if (color != null) {
+                bmp.setPixel(x, y, color.toColor())
+            }
+        }
+    }
+    File("test.tga").writeBitmap(bmp)
+}

src/main/kotlin/Vector.kt

@@ -11,6 +11,8 @@ data class Vector(val x: Float, val y: Float, val z: Float) {
     operator fun unaryMinus(): Vector = Vector(-x, -y, -z)
     operator fun minus(rhs: Vector): Vector = Vector(x - rhs.x, y - rhs.y, z - rhs.z)
     operator fun div(rhs: Float): Vector = Vector(x / rhs, y / rhs, z / rhs)
+
+    infix fun dot(rhs: Vector): Float = x * rhs.x + y * rhs.y + z * rhs.z
 }
 
 operator fun Float.times(rhs: Vector): Vector = rhs * this