# OpenGL Explosions

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Hi, everyone, I'm trying to make explosions for a game I'm writing. The explosion should not take up too much processor time; I'm doing real-time rendering. The explosions will be non-nuclear and both airborne and land-based. I can handle the particles of the exploding object, but I need to know how I should go about drawing the actual fireball. For example, should I do something fancy with OpenGL, or should I draw something with explosion textures? It is possible that the explosions could be different each time, but a predetermined explosion animation would be fine too. Thanks, G

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at the end of this video

a pretty easy way of making accually pretty good looking explosions
they will be really cheap to render also

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Really cool! Those explosions would certainly be acceptable. Where did the explosion come from? I want the same animation!

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You can either render an explosion animation and do some pixel shader magic to make it look volumetric or you can layer several slices of a 3D-rendered explosion animation and blend them in whatever way you like (blurring + additive blending for example). Both methods are pretty cheap.

As to where to get explosion animations... stock footage and effect DVD's for real explosions and you can also render your own in 3D Studio, which has the additional benefit of having full control over the output(alpha + depth information etc.).

Then you can also use a particle system for unique explosions and style, but it takes a lot of tweaking to make them look realistic. Depends on the look and feel of your game if you want to do this.

Maybe post some screen shots for us to see what you're aiming at.

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In the book, Texturing and Modeling: A Procedural Approach, Ken Perlin wrote a section describing a raymarching algorithm for rendering volumetric density functions, and one of the example techniques demonstrated constructing an explosion. He took a spherical shaped density function, where the density was 1 at the center and dropped off to 0 at the radius of the sphere, and distorted the function by applying simple noise-based turbulence to the domain. By animating the turbulence function over time you get a changing billow pattern. By scaling the sphere you can create the effect of the explosion expanding outward.

You could construct a simplified version of the raymarcher (code is given, and the concept is really very simple) to collect densities and colorize the field depending on density; then, by animating the density function of the initial sphere to tend toward 0 over time, you can simulate the explosion dissipating and fading away. By mapping the output density to an appropriate color function that includes black at very low densities, fading into dusky oranges, reds, yellows, and finally white (for very hot, intense explosions) you can generate a fairly decent explosion. Then animate the parameters for turbulence, density and radius over time, rendering into a colormap at each step, to generate the frames of your explosion. You can generate multiple explosions for the various layers to avoid the appearance of repetition. When shading effects are applied to the explosion, you get a turbulent, billowy cloud very much like an explosion.

As an alternative to doing a billboarded explosion of this nature, you could construct a run-time version of the raymarcher and build your explosions on the fly by using this same technique. Might be tricky, as volumetric raymarching is computationally expensive and multiple explosions, unless sampled in a very small value (and thus sacrificing detail) could bring your game to it's knees.

Or you could model an explosion using simple particles. Different components of the explosion would use different particle material settings. The smoke layer would use lots of black particles blended with the scene. The fireball would include particles with low-power reds and oranges additively blended onto the scene. If the low-power color of these reds and oranges includes a non-negative blue component, then as more particles are added, the color will tend toward the white, for high-intensities. In my (somewhat limited) experience, these particle-based explosions tend to be trickier, harder to produce realistic explosions, and may require a lot of heavy experimentation to get good results. However, they can be constructed to be fairly efficient in real-time and allow the generation of randomized, procedural explosions, thus avoiding repetition.

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I like the raymarcher idea. There's already going to be particles in the form of fragments of the exploding object. There's probably only going to be one explosion at a time. Where can I get the source? Or can you give me a small sample program?

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I've been fiddling around a little bit, and achieved some pretty nice results for creating the explosion sprite images as used in the youtube video that somebody linked earlier. For example:

The way I created this:

First, I setup a color gradient that ranges from RGB(0,0,0) to RGB(1,1,1), passing through points where the color is red, orange and yellow. Then I constructed a spherical function with a radius of 1.0 that returns a value of 1.0 at the center and 0 beyond the radius. Then I set up a turbulence modifier attached to the spherical function, with 3 separate Perlin noise modules.

The way the turbulence works is, imagine you are iterating the 2x2x2 cube from (-1,-1,-1) to (1,1,1), and outputing the spherical noise function. If you could envision the output, you would see a 'fuzzy' sphere, smoothly gradient from center outward. By adding a little noise to the input coordinates passed to the sphere function you get a turbulent shape that still maps from 1.0 to 0.0, but the noise added to the input domain distorts the shape from a perfect sphere to a more fluid 'explody' type shape.

Now, I iterated a 'slice' of the distorted sphere right through center, rendering this 2D slice onto a plane. The output value of the input coords is used as an interpolant to lookup the color from the color scale, so that values of 0 (outside the sphere) are black with an alpha of 0, progressing through red, orange, yellow and finally to white at 1.0. The looked-up color was written to a color buffer and the final result saved to an image file. I opened the file in Gimp, copied the whole thing, scaled the copy down, and pasted it a couple times on top of the original to see what it might look like when used as demonstrated in the youtube video linked earlier. The results were pretty neat, all things considered.

I rendered only a single frame, but by animating the various parameters used to generate the sphere and perturb, and by scaling the output of the function downward over time, you can get a roiling effect with the flame 'cooling' toward black and increasing in transparency as it tends toward the 0 end of the color scale. Couple that with some scaling to increase the expansion of the gas cloud, and you could get some pretty neat results.

I implemented all of this using my own custom tools, but if you would like to see the code I used, let me know.

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I'd love that. I think I see how that works, but that is just beautiful.

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I did a writeup and posted some tools in my journal. It's crude, but it works.

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Looks really cool, BTW, and it runs really quickly (1 sec. to render 10 frames and save on my computer), so I think this could work real-time.

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• ### Similar Content

• By mmmax3d
Hi everyone,
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• By mmmax3d
Hi everyone,
I would need some assistance from anyone who has a similar experience
or a nice idea!
I have created a skybox (as cube) and now I need to add a floor/ground.
The skybox is created from cubemap and initially it was infinite.
Now it is finite with a specific size. The floor is a quad in the middle
of the skybox, like a horizon.
I have two problems:
When moving the skybox upwards or downwards, I need to
sample from points even above the horizon while sampling
from the botton at the same time.  I am trying to create a seamless blending of the texture
at the points of the horizon, when the quad is connected
to the skybox. However, I get skew effects. Does anybody has done sth similar?
Is there any good practice?
Thanks everyone!

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• Hello Everyone!
I'm learning openGL, and currently i'm making a simple 2D game engine to test what I've learn so far.  In order to not say to much, i made a video in which i'm showing you the behavior of the rendering.
Video:

What i was expecting to happen, was the player moving around. When i render only the player, he moves as i would expect. When i add a second Sprite object, instead of the Player, this new sprite object is moving and finally if i add a third Sprite object the third one is moving. And the weird think is that i'm transforming the Vertices of the Player so why the transformation is being applied somewhere else?

Take a look at my code:
Sprite Class
(You mostly need to see the Constructor, the Render Method and the Move Method)
#include "Brain.h" #include <glm/gtc/matrix_transform.hpp> #include <vector> struct Sprite::Implementation { //Position. struct pos pos; //Tag. std::string tag; //Texture. Texture *texture; //Model matrix. glm::mat4 model; //Vertex Array Object. VertexArray *vao; //Vertex Buffer Object. VertexBuffer *vbo; //Layout. VertexBufferLayout *layout; //Index Buffer Object. IndexBuffer *ibo; //Shader. Shader *program; //Brains. std::vector<Brain *> brains; //Deconstructor. ~Implementation(); }; Sprite::Sprite(std::string image_path, std::string tag, float x, float y) { //Create Pointer To Implementaion. m_Impl = new Implementation(); //Set the Position of the Sprite object. m_Impl->pos.x = x; m_Impl->pos.y = y; //Set the tag. m_Impl->tag = tag; //Create The Texture. m_Impl->texture = new Texture(image_path); //Initialize the model Matrix. m_Impl->model = glm::mat4(1.0f); //Get the Width and the Height of the Texture. int width = m_Impl->texture->GetWidth(); int height = m_Impl->texture->GetHeight(); //Create the Verticies. float verticies[] = { //Positions //Texture Coordinates. x, y, 0.0f, 0.0f, x + width, y, 1.0f, 0.0f, x + width, y + height, 1.0f, 1.0f, x, y + height, 0.0f, 1.0f }; //Create the Indicies. unsigned int indicies[] = { 0, 1, 2, 2, 3, 0 }; //Create Vertex Array. m_Impl->vao = new VertexArray(); //Create the Vertex Buffer. m_Impl->vbo = new VertexBuffer((void *)verticies, sizeof(verticies)); //Create The Layout. m_Impl->layout = new VertexBufferLayout(); m_Impl->layout->PushFloat(2); m_Impl->layout->PushFloat(2); m_Impl->vao->AddBuffer(m_Impl->vbo, m_Impl->layout); //Create the Index Buffer. m_Impl->ibo = new IndexBuffer(indicies, 6); //Create the new shader. m_Impl->program = new Shader("Shaders/SpriteShader.shader"); } //Render. void Sprite::Render(Window * window) { //Create the projection Matrix based on the current window width and height. glm::mat4 proj = glm::ortho(0.0f, (float)window->GetWidth(), 0.0f, (float)window->GetHeight(), -1.0f, 1.0f); //Set the MVP Uniform. m_Impl->program->setUniformMat4f("u_MVP", proj * m_Impl->model); //Run All The Brains (Scripts) of this game object (sprite). for (unsigned int i = 0; i < m_Impl->brains.size(); i++) { //Get Current Brain. Brain *brain = m_Impl->brains[i]; //Call the start function only once! if (brain->GetStart()) { brain->SetStart(false); brain->Start(); } //Call the update function every frame. brain->Update(); } //Render. window->GetRenderer()->Draw(m_Impl->vao, m_Impl->ibo, m_Impl->texture, m_Impl->program); } void Sprite::Move(float speed, bool left, bool right, bool up, bool down) { if (left) { m_Impl->pos.x -= speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(-speed, 0, 0)); } if (right) { m_Impl->pos.x += speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(speed, 0, 0)); } if (up) { m_Impl->pos.y += speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(0, speed, 0)); } if (down) { m_Impl->pos.y -= speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(0, -speed, 0)); } } void Sprite::AddBrain(Brain * brain) { //Push back the brain object. m_Impl->brains.push_back(brain); } pos *Sprite::GetPos() { return &m_Impl->pos; } std::string Sprite::GetTag() { return m_Impl->tag; } int Sprite::GetWidth() { return m_Impl->texture->GetWidth(); } int Sprite::GetHeight() { return m_Impl->texture->GetHeight(); } Sprite::~Sprite() { delete m_Impl; } //Implementation Deconstructor. Sprite::Implementation::~Implementation() { delete texture; delete vao; delete vbo; delete layout; delete ibo; delete program; }
Renderer Class
#include "Renderer.h" #include "Error.h" Renderer::Renderer() { } Renderer::~Renderer() { } void Renderer::Draw(VertexArray * vao, IndexBuffer * ibo, Texture *texture, Shader * program) { vao->Bind(); ibo->Bind(); program->Bind(); if (texture != NULL) texture->Bind(); GLCall(glDrawElements(GL_TRIANGLES, ibo->GetCount(), GL_UNSIGNED_INT, NULL)); } void Renderer::Clear(float r, float g, float b) { GLCall(glClearColor(r, g, b, 1.0)); GLCall(glClear(GL_COLOR_BUFFER_BIT)); } void Renderer::Update(GLFWwindow *window) { /* Swap front and back buffers */ glfwSwapBuffers(window); /* Poll for and process events */ glfwPollEvents(); }
#shader vertex #version 330 core layout(location = 0) in vec4 aPos; layout(location = 1) in vec2 aTexCoord; out vec2 t_TexCoord; uniform mat4 u_MVP; void main() { gl_Position = u_MVP * aPos; t_TexCoord = aTexCoord; } #shader fragment #version 330 core out vec4 aColor; in vec2 t_TexCoord; uniform sampler2D u_Texture; void main() { aColor = texture(u_Texture, t_TexCoord); } Also i'm pretty sure that every time i'm hitting the up, down, left and right arrows on the keyboard, i'm changing the model Matrix of the Player and not the others.

Window Class:
#include "Window.h" #include <GL/glew.h> #include <GLFW/glfw3.h> #include "Error.h" #include "Renderer.h" #include "Scene.h" #include "Input.h" //Global Variables. int screen_width, screen_height; //On Window Resize. void OnWindowResize(GLFWwindow *window, int width, int height); //Implementation Structure. struct Window::Implementation { //GLFW Window. GLFWwindow *GLFW_window; //Renderer. Renderer *renderer; //Delta Time. double delta_time; //Frames Per Second. int fps; //Scene. Scene *scnene; //Input. Input *input; //Deconstructor. ~Implementation(); }; //Window Constructor. Window::Window(std::string title, int width, int height) { //Initializing width and height. screen_width = width; screen_height = height; //Create Pointer To Implementation. m_Impl = new Implementation(); //Try initializing GLFW. if (!glfwInit()) { std::cout << "GLFW could not be initialized!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); exit(-1); } //Setting up OpenGL Version 3.3 Core Profile. glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); /* Create a windowed mode window and its OpenGL context */ m_Impl->GLFW_window = glfwCreateWindow(width, height, title.c_str(), NULL, NULL); if (!m_Impl->GLFW_window) { std::cout << "GLFW could not create a window!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); glfwTerminate(); exit(-1); } /* Make the window's context current */ glfwMakeContextCurrent(m_Impl->GLFW_window); //Initialize GLEW. if(glewInit() != GLEW_OK) { std::cout << "GLEW could not be initialized!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); glfwTerminate(); exit(-1); } //Enabling Blending. GLCall(glEnable(GL_BLEND)); GLCall(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)); //Setting the ViewPort. GLCall(glViewport(0, 0, width, height)); //**********Initializing Implementation**********// m_Impl->renderer = new Renderer(); m_Impl->delta_time = 0.0; m_Impl->fps = 0; m_Impl->input = new Input(this); //**********Initializing Implementation**********// //Set Frame Buffer Size Callback. glfwSetFramebufferSizeCallback(m_Impl->GLFW_window, OnWindowResize); } //Window Deconstructor. Window::~Window() { delete m_Impl; } //Window Main Loop. void Window::MainLoop() { //Time Variables. double start_time = 0, end_time = 0, old_time = 0, total_time = 0; //Frames Counter. int frames = 0; /* Loop until the user closes the window */ while (!glfwWindowShouldClose(m_Impl->GLFW_window)) { old_time = start_time; //Total time of previous frame. start_time = glfwGetTime(); //Current frame start time. //Calculate the Delta Time. m_Impl->delta_time = start_time - old_time; //Get Frames Per Second. if (total_time >= 1) { m_Impl->fps = frames; total_time = 0; frames = 0; } //Clearing The Screen. m_Impl->renderer->Clear(0, 0, 0); //Render The Scene. if (m_Impl->scnene != NULL) m_Impl->scnene->Render(this); //Updating the Screen. m_Impl->renderer->Update(m_Impl->GLFW_window); //Increasing frames counter. frames++; //End Time. end_time = glfwGetTime(); //Total time after the frame completed. total_time += end_time - start_time; } //Terminate GLFW. glfwTerminate(); } //Load Scene. void Window::LoadScene(Scene * scene) { //Set the scene. m_Impl->scnene = scene; } //Get Delta Time. double Window::GetDeltaTime() { return m_Impl->delta_time; } //Get FPS. int Window::GetFPS() { return m_Impl->fps; } //Get Width. int Window::GetWidth() { return screen_width; } //Get Height. int Window::GetHeight() { return screen_height; } //Get Input. Input * Window::GetInput() { return m_Impl->input; } Renderer * Window::GetRenderer() { return m_Impl->renderer; } GLFWwindow * Window::GetGLFWindow() { return m_Impl->GLFW_window; } //Implementation Deconstructor. Window::Implementation::~Implementation() { delete renderer; delete input; } //OnWindowResize void OnWindowResize(GLFWwindow *window, int width, int height) { screen_width = width; screen_height = height; //Updating the ViewPort. GLCall(glViewport(0, 0, width, height)); }
Brain Class
#include "Brain.h" #include "Sprite.h" #include "Window.h" struct Brain::Implementation { //Just A Flag. bool started; //Window Pointer. Window *window; //Sprite Pointer. Sprite *sprite; }; Brain::Brain(Window *window, Sprite *sprite) { //Create Pointer To Implementation. m_Impl = new Implementation(); //Initialize Implementation. m_Impl->started = true; m_Impl->window = window; m_Impl->sprite = sprite; } Brain::~Brain() { //Delete Pointer To Implementation. delete m_Impl; } void Brain::Start() { } void Brain::Update() { } Window * Brain::GetWindow() { return m_Impl->window; } Sprite * Brain::GetSprite() { return m_Impl->sprite; } bool Brain::GetStart() { return m_Impl->started; } void Brain::SetStart(bool value) { m_Impl->started = value; } Script Class (Its a Brain Subclass!!!)
#include "Script.h" Script::Script(Window *window, Sprite *sprite) : Brain(window, sprite) { } Script::~Script() { } void Script::Start() { std::cout << "Game Started!" << std::endl; } void Script::Update() { Input *input = this->GetWindow()->GetInput(); Sprite *sp = this->GetSprite(); //Move this sprite. this->GetSprite()->Move(200 * this->GetWindow()->GetDeltaTime(), input->GetKeyDown("left"), input->GetKeyDown("right"), input->GetKeyDown("up"), input->GetKeyDown("down")); std::cout << sp->GetTag().c_str() << ".x = " << sp->GetPos()->x << ", " << sp->GetTag().c_str() << ".y = " << sp->GetPos()->y << std::endl; }
Main:
#include "SpaceShooterEngine.h" #include "Script.h" int main() { Window w("title", 600,600); Scene *scene = new Scene(); Sprite *player = new Sprite("Resources/Images/player.png", "Player", 100,100); Sprite *other = new Sprite("Resources/Images/cherno.png", "Other", 400, 100); Sprite *other2 = new Sprite("Resources/Images/cherno.png", "Other", 300, 400); Brain *brain = new Script(&w, player); player->AddBrain(brain); scene->AddSprite(player); scene->AddSprite(other); scene->AddSprite(other2); w.LoadScene(scene); w.MainLoop(); return 0; }

I literally can't find what is wrong. If you need more code, ask me to post it. I will also attach all the source files.
Brain.cpp
Error.cpp
IndexBuffer.cpp
Input.cpp
Renderer.cpp
Scene.cpp
Sprite.cpp
Texture.cpp
VertexArray.cpp
VertexBuffer.cpp
VertexBufferLayout.cpp
Window.cpp
Brain.h
Error.h
IndexBuffer.h
Input.h
Renderer.h
Scene.h
SpaceShooterEngine.h
Sprite.h
Texture.h
VertexArray.h
VertexBuffer.h
VertexBufferLayout.h
Window.h

• Hello fellow programmers,
For a couple of days now i've decided to build my own planet renderer just to see how floating point precision issues
can be tackled. As you probably imagine, i've quickly faced FPP issues when trying to render absurdly large planets.

I have used the classical quadtree LOD approach;
I've generated my grids with 33 vertices, (x: -1 to 1, y: -1 to 1, z = 0).
Each grid is managed by a TerrainNode class that, depending on the side it represents (top, bottom, left right, front, back),
creates a special rotation-translation matrix that moves and rotates the grid away from the origin so that when i finally
normalize all the vertices on my vertex shader i can get a perfect sphere.
T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, 1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(180.0), glm::dvec3(1.0, 0.0, 0.0)); sides[0] = new TerrainNode(1.0, radius, T * R, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_FRONT)); T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, -1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(0.0), glm::dvec3(1.0, 0.0, 0.0)); sides[1] = new TerrainNode(1.0, radius, R * T, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_BACK)); // So on and so forth for the rest of the sides As you can see, for the front side grid, i rotate it 180 degrees to make it face the camera and push it towards the eye;
the back side is handled almost the same way only that i don't need to rotate it but simply push it away from the eye.
The same technique is applied for the rest of the faces (obviously, with the proper rotations / translations).
The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as r_Grid'.
// spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The r_ModelViewProjection' matrix is generated on the CPU in this manner.
// No the most efficient way, but it works. glm::dmat4 Camera::getMatrix() { // Create the view matrix // Roll, Yaw and Pitch are all quaternions. glm::dmat4 View = glm::toMat4(Roll) * glm::toMat4(Pitch) * glm::toMat4(Yaw); // The model matrix is generated by translating in the oposite direction of the camera. glm::dmat4 Model = glm::translate(glm::dmat4(1.0), -Position); // Projection = glm::perspective(fovY, aspect, zNear, zFar); // zNear = 0.1, zFar = 1.0995116e12 return Projection * View * Model; } I managed to get rid of z-fighting by using a technique called Logarithmic Depth Buffer described in this article; it works amazingly well, no z-fighting at all, at least not visible.
Each frame i'm rendering each node by sending the generated matrices this way.
// set the r_ModelViewProjection uniform // Sneak in the mRadiusMatrix which is a matrix that contains the radius of my planet. Shader::setUniform(0, Camera::getInstance()->getMatrix() * mRadiusMatrix); // set the r_Grid matrix uniform i created earlier. Shader::setUniform(1, r_Grid); grid->render(); My planet's radius is around 6400000.0 units, absurdly large, but that's what i really want to achieve;
Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
of the planet the rounding errors start to kick in giving me that lovely stairs effect.
I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
getting rid of those rounding errors.

My question is how can i achieve this relative to camera rendering in my scenario here?
I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
I only use double on the CPU side where i also do most of the matrix multiplications.
As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).

Thank you for your suggestions!