This presentation regards working with graphic applications, and in particular it deals with OpenGL's texture direct memory access. Presentation by Rostyslav Lesovyi, Software engineer, GlobalLogic. Mobile TechTalk, Lviv, 2014. More details - www.globallogic.com.ua/press-releases/mobile-techtalk-lviv/

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by Rostyslav Lesovyi
OpenGL's texture DMA
DMA stands for Direct Memory Access

2. ©2013 GlobalLogic Inc. CONFIDENTIAL

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• Async texture upload
• Rapid updates of texture or its parts
• Texture data download
Problems

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• Simple download/upload
• Shared OpenGL contexts
• PBO (Pixel Buffer Objects)
• EGLImage and GraphicBuffer
Solutions

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Pros:
• very easy to use and understand
Cons:
• super slow!!!
• operates in a single thread
• glTexImage2D/glTexSubImage2D for upload
• glReadPixels for download
Simple download/upload

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• create background thread
• create shared OpenGL context
• attach context to background thread
• use glTexImage2D, glTexSubImage2D or glReadPixels
What to do
Shared OpenGL contexts

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EGLContext context =
egl.eglCreateContext(display, config, parentContext, null);
EGLSurface surface =
egl.eglCreatePbufferSurface(display, config, surfaceAttributes);
Shared context creation:
Shared OpenGL contexts

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EGLContext context =
egl.eglCreateContext(display, config, parentContext, null);
EGLSurface surface =
egl.eglCreatePbufferSurface(display, config, surfaceAttributes);
Shared OpenGL contexts

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Pros:
• relatively easy to use
• full threading support
Cons:
• relying on slow functions
Shared OpenGL contexts
More info:
https://github.com/pcwalton/test-async-texture-upload

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Pixel Buffer Objects

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Pixel Buffer Objects
Pros:
• relatively easy to use
• supports asynchronous upload/download
Cons:
• Android 4.3+ / OpenGL ES 3.0
• hard to use for two-ways texture updates
• still copies from PBO to CPU and vice versa
More info:
http://www.songho.ca/opengl/gl_pbo.html

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EGLImage and GraphicBuffer
Regular PC
CPU GPU
CPU Memory GPU Memory
Copy
Mobile device, AMD APUs, etc...
CPU GPU
Shared Memory
= Texture image data (actual pixels)

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EGLImage and GraphicBuffer
Pros:
• direct access to texture’s pixel data
• can be accessed by any thread
• supported by Android 2.0.1+
Cons:
• requires NDK
• requires usage of ARM library
More info:
https://wiki.mozilla.org/Platform/GFX/Gralloc

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Q&A

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Thank you