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Adventures in game development

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Really weird bug: Emscripten / OpenGL shader related


This is just a quick short entry.

Today I tried to compile a small but fully working OpenGL ES 2 shader related code in Emscripten. It didn't work. After a LOT of time debugging I found out that if I call [font='courier new']glBindAttributeLocation(...)[/font] BEFORE actually linking the shader programit works perfectly. So the following code works fine:[code=auto:7]....glAttachShader(_programID, _fragmentShaderID);glAttachShader(_programID, _vertexShaderID);glBindAttribLocation(_programID, VERTEX_ARRAY, "a_position");glBindAttribLocation(_programID, COLOR_ARRAY, "a_color");glLinkProgram(_programID);.......
BUT the following code will DID NOT work with emscripten WebGL:[code=auto:7]....glAttachShader(_programID, _fragmentShaderID);glAttachShader(_programID, _vertexShaderID);glLinkProgram(_programID);glBindAttribLocation(_programID, VERTEX_ARRAY, "a_position");glBindAttribLocation(_programID, COLOR_ARRAY, "a_color");.......
So the best way is to get pre bound attribute location using use [font='courier new']glGetAttribLocation(..)[/font] rather than manually binding it:[code=auto:7]....if(!LoadProgramFromFile("Default.vert", "Default.frag")){ printf("Error Error loading program from file...\n"); return false;} _a_positionLoc = glGetAttribLocation(_programID, "a_position"); _a_color = glGetAttribLocation(_programID, "a_color");....
This may save you a LOT of headache

Happy coding !





Making cross platform games - Experimentation


This is my first ever journal post here on gamedev. I will discuss about doing an experiment to find as cross-platform development environment as possible!

For my next game i've decided to make it very "cross-platform" and port to many platforms (initially probably 2-3 ). Entire game code will be written in C++ and OpenGL ES 2.0. Since this is my first attempt, I really tend to keep the game as simple as possible . Following platforms are in the target list:

1) Desktop (Win / Mac / Linux)
Since direct support for GL ES is weak on desktops specially Windows, I am considering 3rd party EGL bindings. PowerVR and ATI SDKs for OpenGL ES 2.0 are good options as they come with GLES 2.0 simulators. But an alternative option I found really tempting was "Angle". It provides headers and libraries to develop GLES 2.0 applications on Windows. It appears light weight, under the hood angle translates GLES calls to DirectX. For basic window management one could write small amount of system-specific code. I will discuss this in future blog post after some experimentation.

2) Android
Android SDK and NDK supports GLES 2.0 and let you write entire thing in C++. So the porting won't face any real issues except to write the window initialization and little system specific code.

3) iOS
Exactly the same as android. Native support for GLES 2.0. Xcode also has a nice built-in emulator. Can easily merge C++ with Objective-C.

4) WebGL
This is probably the easiest . Use emscripten to convert the entire C++ / GLES 2.0 game to HTML5 with almost no modifications. Entire Unreal 4 engine has been ported to HTML5! Emscripten has very good built-in support for GLES 2.0 and GLFW. The community is very active and lots of material available on the internet.

5) Flash
You can port you existing C++/GLES code to Flash using Crossbridge. Epic have ported their Unreal 3 engine and you can check out the demo. But i think that this is pretty much dead. It is no longer being regularly maintained and an inactive community. But this may be OK for small 2D games that I intend to make.

6) Black berry
Black berry provides their own SDK and let you to write Native code in C++. Porting should be relatively easy.

OUYA development is almost like android. They also provide their own SDK.

8) Nook
9) Various consoles
Will look at these in the future.

Majority of the mobile devices support OpenGL ES 2.0. It appears to be a good idea to write a single portable GLES 2.0 renderer which would work on almost all the devices without any changes. It even works with traditional desktops (even though ES2 is not as powerful as the full blown OpenGL but it is pretty good for 2D games). But finding a cross-platform solution for Sound, context management, input, APIs for quering resources etc might be a real challenge.

Next time i'll post the results of this experiment and list down libraries that I found to be the most portable across all platforms.

Happy coding...




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