• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0

OpenGL Fade In/Out Effect

5 posts in this topic

I couldn't find an up to date tutorial about it and I'm not sure how this can be done.


I have an image with a text (the game title), it's a 200x100 BMP image.

Some pixels are have the (255, 0, 255) color and during the loading, I set the alpha value to 255 when I find these values.


In my initialization code:



An my pixel shader:

    void main()
        color = texture2D(objectTexture, UV).rgba;


So it's displaying fine, but I want to add an effect of fade in/out on it, but just the title, nothing else.

The "regular" way I found is to create a polygon that covers the image and change it's alpha, but then the things behind it are also faded (and you can notice the polygon around it).


Another way is to create a pixel shader that receives an alpha value, and I send these values I calculate based on the time, so I have in the pixel shader:


    in float alpha;
    void main()
        color = vec4(texture2D(objectTexture, UV).rgb, alpha);


But this would surely mess the already transparent pixels since I'm discarding the image's alpha values.


I found about the command glTexEnv() but I couldn't find it in the OpenGL4.0 reference pages, so I'm guessing it's outdated and I couldn't find the updated one.


How can I get this effect?


Share this post

Link to post
Share on other sites

Hmm I think I got it, I just added an 

if(color.w == 1)
    color.w = alpha; //the value I sent

I've read that if statements should be avoided in the shaders but I couldn't think of any other option, is there any better way to do this?


Edit: Also, this made me wonder... I had to create a separate programID that receives the alpha and uses it for the fading effect, but what am I supposed to do then if I have an object with a material type of Y (a specific shader) and I want to add this fading effect to it? (Like those effects of characters going stealth)


Am I supposed to create each of these effects plus an alternative version for the alpha effect?

Edited by Danicco

Share this post

Link to post
Share on other sites

I highly recommend vertex color blending. In this case you would have a quad or maybe a set of quads that represent your titles.


By blending a vertex alpha with the texture sample, you will get the desired result without using the branching statement mentioned, and at a much better performance.


In this case you would set all the vertices to white color, and just manipulate the alpha of these vertices. Your shader would multiply the vertex color and the texture lookup.


Let me know if you have any issues.


Share this post

Link to post
Share on other sites

Oh, and if instead of fading alpha you want to fade from white / black or to white or black, use a simple quad that covers your desired area and draw it on top.


Set the colors to white/black as desired and just tweak the alpha. A simple blend operation like EaseIn / EaseOut will give you even better results than linear blending. ActionScript tutorials are all over the place that will give you these easing equations.


Share this post

Link to post
Share on other sites

Hmm I couldn't find practical examples of this effect you mentioned, but I tried to do this:



uniform vec4 vertexAlpha;
out vec4 pixelAlpha;
void main()
    //other stuff too
    pixelAlpha = vertexAlpha;


in vec4 pixelAlpha;
out vec4 color;
void main()
    color = texture2D(objectTexture, UV).rgba * pixelAlpha;

And in the code I have a float[4] for the alphaChannel values (set to white, 1 in alpha), but when I change the alpha my quad is going blacker and blacker, but leaving the black quad on screen instead of disappearing, so I think I'm off something...


Edit: Ah, I also think it's relevant to mention that the texture already has an alpha value (though I manually set them all to 255) and I'm using:


This would work if I always had a black screen and want to fade in/out, but I'm trying to achieve the fade in/out with transparency (for example with a background image behind, and then an image fades in/out over it).

How can I get this effect?


Edit2: Reading here (http://www.opengl.org/archives/resources/faq/technical/transparency.htm) I noticed I was trying to render the transparent object first, but this might be causing/being caused by some other problem... I have a background image and a small quad image on screen, and I'm drawing them in the order: Background -> Quad.

But even with blend disabled, I'm only getting the Background displayed.

I only get the see the Quad if I draw them in the order Quad -> Background.


Am I doing something terribly wrong here for this to happen?


Edit3: I disabled glEnable(GL_DEPTH_TEST) before drawing 2Ds objects and the effect is finally showing! Thank you very much!

Edited by Danicco

Share this post

Link to post
Share on other sites

I made a fade in/out for a simple polygon that fades in and out, because of the variation of the Z coordinate of that polygon.

#version 330 core

in vec4 fragColor;

out vec4 finalColor;

in float zPos;

void main()
	vec4 color = fragColor;

	float partA = -1.0 * zPos;
	float partB = partA - 7.0;
	color.a = 1.0 - partB;

	finalColor = color;

zPos is always negative in my case, so in partA I make it a positive value, then in partB I decrease it by 7. The value in partB is used to get alpha value for the color of the polygon.


The initial value of zPos is -8.0, then it increases to -7.0. This is a fade in. Then the zPos from value -7.0 dereases again to -8.0. This way i get a fade out.




In this video a recorded the game that uses this fragment shader for fading in/out the squares that are in background.


Hope this will help you to write the right shader for your problem. :)


P.S. Sorry for my english, if i made any mistakes.


Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
Followers 0

  • Similar Content

    • By Toastmastern
      So it's been a while since I took a break from my whole creating a planet in DX11. Last time around I got stuck on fixing a nice LOD.
      A week back or so I got help to find this:
      In general this is what I'm trying to recreate in DX11, he that made that planet LOD uses OpenGL but that is a minor issue and something I can solve. But I have a question regarding the code
      He gets the position using this row
      vec4d pos = b.var.vec4d["position"]; Which is then used further down when he sends the variable "center" into the drawing function:
      if (pos.len() < 1) pos.norm(); world::draw(vec3d(pos.x, pos.y, pos.z));  
      Inside the draw function this happens:
      draw_recursive(p3[0], p3[1], p3[2], center); Basically the 3 vertices of the triangle and the center of details that he sent as a parameter earlier: vec3d(pos.x, pos.y, pos.z)
      Now onto my real question, he does vec3d edge_center[3] = { (p1 + p2) / 2, (p2 + p3) / 2, (p3 + p1) / 2 }; to get the edge center of each edge, nothing weird there.
      But this is used later on with:
      vec3d d = center + edge_center[i]; edge_test[i] = d.len() > ratio_size; edge_test is then used to evaluate if there should be a triangle drawn or if it should be split up into 3 new triangles instead. Why is it working for him? shouldn't it be like center - edge_center or something like that? Why adding them togheter? I asume here that the center is the center of details for the LOD. the position of the camera if stood on the ground of the planet and not up int he air like it is now.

      Full code can be seen here:
      If anyone would like to take a look and try to help me understand this code I would love this person. I'm running out of ideas on how to solve this in my own head, most likely twisted it one time to many up in my head
      Thanks in advance
    • By fllwr0491
      I googled around but are unable to find source code or details of implementation.
      What keywords should I search for this topic?
      Things I would like to know:
      A. How to ensure that partially covered pixels are rasterized?
         Apparently by expanding each triangle by 1 pixel or so, rasterization problem is almost solved.
         But it will result in an unindexable triangle list without tons of overlaps. Will it incur a large performance penalty?
      B. A-buffer like bitmask needs a read-modiry-write operation.
         How to ensure proper synchronizations in GLSL?
         GLSL seems to only allow int32 atomics on image.
      C. Is there some simple ways to estimate coverage on-the-fly?
         In case I am to draw 2D shapes onto an exisitng target:
         1. A multi-pass whatever-buffer seems overkill.
         2. Multisampling could cost a lot memory though all I need is better coverage.
            Besides, I have to blit twice, if draw target is not multisampled.
    • By mapra99

      I am working on a recent project and I have been learning how to code in C# using OpenGL libraries for some graphics. I have achieved some quite interesting things using TAO Framework writing in Console Applications, creating a GLUT Window. But my problem now is that I need to incorporate the Graphics in a Windows Form so I can relate the objects that I render with some .NET Controls.

      To deal with this problem, I have seen in some forums that it's better to use OpenTK instead of TAO Framework, so I can use the glControl that OpenTK libraries offer. However, I haven't found complete articles, tutorials or source codes that help using the glControl or that may insert me into de OpenTK functions. Would somebody please share in this forum some links or files where I can find good documentation about this topic? Or may I use another library different of OpenTK?

    • By Solid_Spy
      Hello, I have been working on SH Irradiance map rendering, and I have been using a GLSL pixel shader to render SH irradiance to 2D irradiance maps for my static objects. I already have it working with 9 3D textures so far for the first 9 SH functions.
      In my GLSL shader, I have to send in 9 SH Coefficient 3D Texures that use RGBA8 as a pixel format. RGB being used for the coefficients for red, green, and blue, and the A for checking if the voxel is in use (for the 3D texture solidification shader to prevent bleeding).
      My problem is, I want to knock this number of textures down to something like 4 or 5. Getting even lower would be a godsend. This is because I eventually plan on adding more SH Coefficient 3D Textures for other parts of the game map (such as inside rooms, as opposed to the outside), to circumvent irradiance probe bleeding between rooms separated by walls. I don't want to reach the 32 texture limit too soon. Also, I figure that it would be a LOT faster.
      Is there a way I could, say, store 2 sets of SH Coefficients for 2 SH functions inside a texture with RGBA16 pixels? If so, how would I extract them from inside GLSL? Let me know if you have any suggestions ^^.
    • By KarimIO
      EDIT: I thought this was restricted to Attribute-Created GL contexts, but it isn't, so I rewrote the post.
      Hey guys, whenever I call SwapBuffers(hDC), I get a crash, and I get a "Too many posts were made to a semaphore." from Windows as I call SwapBuffers. What could be the cause of this?
      Update: No crash occurs if I don't draw, just clear and swap.
      static PIXELFORMATDESCRIPTOR pfd = // pfd Tells Windows How We Want Things To Be { sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor 1, // Version Number PFD_DRAW_TO_WINDOW | // Format Must Support Window PFD_SUPPORT_OPENGL | // Format Must Support OpenGL PFD_DOUBLEBUFFER, // Must Support Double Buffering PFD_TYPE_RGBA, // Request An RGBA Format 32, // Select Our Color Depth 0, 0, 0, 0, 0, 0, // Color Bits Ignored 0, // No Alpha Buffer 0, // Shift Bit Ignored 0, // No Accumulation Buffer 0, 0, 0, 0, // Accumulation Bits Ignored 24, // 24Bit Z-Buffer (Depth Buffer) 0, // No Stencil Buffer 0, // No Auxiliary Buffer PFD_MAIN_PLANE, // Main Drawing Layer 0, // Reserved 0, 0, 0 // Layer Masks Ignored }; if (!(hDC = GetDC(windowHandle))) return false; unsigned int PixelFormat; if (!(PixelFormat = ChoosePixelFormat(hDC, &pfd))) return false; if (!SetPixelFormat(hDC, PixelFormat, &pfd)) return false; hRC = wglCreateContext(hDC); if (!hRC) { std::cout << "wglCreateContext Failed!\n"; return false; } if (wglMakeCurrent(hDC, hRC) == NULL) { std::cout << "Make Context Current Second Failed!\n"; return false; } ... // OGL Buffer Initialization glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT); glBindVertexArray(vao); glUseProgram(myprogram); glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_SHORT, (void *)indexStart); SwapBuffers(GetDC(window_handle));  
  • Popular Now