A technical blog from Daniel Rákos (aka aqnuep)
Posts tagged fragment shader
OpenGL vs DirectX: The War Is Far From Over
Oct 7th
The War Is Far From Over
I’ve chosen the title based on the popular article that tries to prove that OpenGL lost the war against Direct3D. To be honest, I didn’t really like the article at all. First, because it compared OpenGL 3 which targeted Shader Model 4.0 hardware and DirectX 11 which targeted Shader Model 5.0 hardware. Besides that, as we will see, the war is really far from over… This article aims to list the most important features introduced by OpenGL 3.x, OpenGL 4.x, Direct3D 10, Direct3D 11 and we will also talk about the promised features of the upcoming Direct3D 11.1 to be fair with DirectX 
An introduction to OpenGL 4.2
Aug 28th
After the release of the OpenGL 4.1 specification the Khronos Group slowed down the pace a little bit but they didn’t left OpenGL developers without a new specification version for too long as a few weeks ago they’ve released OpenGL 4.2. The new version of the specification brings several API improvements as well as exposes some important pieces of hardware functionality that makes OpenGL 4.x class hardware a great step forward in GPU history. This article aims to present the newly introduced features in the latest version of the OpenGL specification and, as a few months ago I wrote an article about Suggestions for OpenGL 4.2 and beyond, I will write a few words about how does the new specification reflect my forecast.
Frei-Chen edge detector
Jan 30th
Frei-Chen edge detector
In this article, I would like to present you an edge detection algorithm that shares similar performance characteristics like the well-known Sobel operator but provides slightly better edge detection and can be seamlessly extended with little to no performance overhead to also detect corners alongside with edges. The algorithm works on a 3×3 texel footprint similarly like the Sobel filter but applies a total of nine convolution masks over the image that can be used for either edge or corner detection. The article presents the mathematical background that is needed to implement the edge detector and provides a reference implementation written in C/C++ using OpenGL that showcases both the Frei-Chen and the Sobel edge detection filter applied to the same image.
Suggestions for OpenGL 4.2 and beyond
Nov 14th
The Khronos Group did a great job in the last few years to once again prove that OpenGL is still in game and that it can become the ultimate graphics API of choice, if it is not that already. However, we must note that it is not quite yet true that OpenGL 4.1 is a superset of its competitor, DirectX 11. We still have some holes that still have to be filled and I think the ARB should not stop just there as there is much more potential in the current hardware architectures than that is currently exposed by any graphics API so establishing the future of OpenGL should start by going one step further than DX11. In this article I would like to present my vision of items of importance that should be included in the next revision of the specification and how I see the future of OpenGL.
Hierarchical-Z map based occlusion culling
Oct 19th
OpenGL 4.0 - Mountains demo
Hierarchical-Z is a well known and standard feature of modern GPUs that allows them to speed up depth testing by rejecting large group of incoming fragments using a reduced and compressed version of the depth buffer that resides in on-chip memory. The technique presented in this article uses the same basic idea to allow batched occlusion culling for large amount of individual objects using a geometry shader without the need of any CPU intervention that is unavoidable using traditional occlusion queries. The article also provides a reference implementation in the form of the OpenGL 4.0 Mountains demo that uses the technique for culling thousands of object instances.
Efficient Gaussian blur with linear sampling
Sep 7th
Gaussian blur
Gaussian blur is an image space effect that is used to create a softly blurred version of the original image. This image then can be used by more sophisticated algorithms to produce effects like bloom, depth-of-field, heat haze or fuzzy glass. In this article I will present how to take advantage of the various properties of the Gaussian filter to create an efficient implementation as well as a technique that can greatly improve the performance of a naive Gaussian blur filter implementation by taking advantage of bilinear texture filtering to reduce the number of necessary texture lookups. While the article focuses on the Gaussian blur filter, most of the principles presented are valid for most convolution filters used in real-time graphics.
A brief preview of the new features introduced by OpenGL 3.3 and 4.0
Mar 15th
The Khronos Group continues the progress of streamlining the OpenGL API. One very important step in this battle has been made just a few days ago by releasing two concurrent core releases of the OpenGL specification, namely version 3.3 and 4.0. This is a major update of the standard containing many revolutionary additions to the tool-set of OpenGL that need careful examination. In this article I would like to talk about these new features trying to point out their importance and touching also some practical use case scenarios.
Instance culling using geometry shaders
Feb 8th
OpenGL 3.2 - Nature
Since the appearance of Shader Model 4.0 people wonder how to take advantage of the newly introduced programmable pipeline stage. The most important feature enabled by geometry shaders is that one can change the amount of emitted primitives inside the pipeline. The first thing that a naive developer would try to do with it is geometry tesselation. However, the new shader performs very bad when used for tesselation in a real life scenario even though there are demos show casting this possibility. If we take a closer look at the new feature we observe that the most revolutionary in it is not that it can raise the number of emitted primitives but that it can discard them. This article would like to present a rendering technique that takes advantage of this aspect of geometry shaders to enable the GPU accelerated culling of higher order primitives.