OpenGL Evolution & JOGL

+ +

OpenGL Evolution

+ +

+OpenGL is an application programming interface (API) giving application developers +access to hardware accelerated 3D rendering (incl. 2D).

+ +

+SGI released the first OpenGL specification in January 1992. +Since this point OpenGL 1.x constantly evolved, first under the ARB and later under the Khronos Group.

+ +

+The OpenGL API was specified with the objective of maximal hardware acceleration, +ie the API functions shall be implemented in hardware - as much as possible. +Further more, OpenGL is considered a vendor neutral and platform agnostic API, +ie should run anywhere, implemented by all 3D GPU manufacturer.

+ +

+Up until OpenGL 1.5, released in July 2003, the core API reflected the so called fixed function pipeline (FFP). +FFP allowed a user to pass triangles, textures and attributes to the GPU. +The attributes had to be utilized to select predefined function of rendering, +hence the name fixed function.

+ +

+Around 2000 new types of GPU hardware evolved, +allowing custom code running on the GPU hardware, +instead of being restricted to the fixed function rendering code.

+ +

+To allow processing of such user defined algorithms on the GPU, +in 2002 the programmable shader pipeline (PSP) was introduced. +The OpenGL Shading Language (GLSL) used to write such shader programs +became an extension to OpenGL 1.4.

+ +

+GLSL allows users to +

write ANSI-C like shader programs
compile shader programs
upload shader programs to the GPU

+ +

+The shader, executed on the GPU, transform the +triangle position and determine the pixel color.

+ +

+Within this process, the shader may use any form of data, +arrays, textures and framebuffer. +It reads it, computes and stores the result in the target framebuffer(s), +hence the name programmable.

+ +

+In September 2004, GLSL subsumed into the core OpenGL 2.0 API, +hence OpenGL 2.0 supported both, FFP and PSP.

+ +

+The desire to utilize OpenGL on embedded devices increased +the more 3D capabilities appeared.

+ +

+Around 2005 a subset of the FFP of OpenGL 1.3 +for embedded systems was released, OpenGL ES 1.0.

+ +

+In March 2007 a programmable shader (PSP) only subset of OpenGL 2.0 +for embedded systems was released.

+ +

+In July 2010 OpenGL 4.1 was released and it's core profile +is fully compatible to OpenGL ES 2.0.

+ +

+Today, desktop and embedded GPU's implement the programmatic shader (PSP) +based rendering.

+ +

+Still the fixed function subset is provided by most drivers. +However, since the hardware itself does not implement such functionality anymore, +it is completely implemented in software by the OpenGL driver.

+ +

+This leads to the conclusion it is best advised for OpenGL applications +to avoid the FFP, but using the PSP. This allows the implementor +to utilize application level optimization which usually cannot be reached +by the very generic implemented FFP in the OpenGL drivers.

+ +

JOGL & The OpenGL Evolution

+Like GL4Java, the 1st JOGL release 1.x +mapped OpenGL in one interface. This architecture was feasible and correct until the new OpenGL +profiles surfaced. There was only one unique way to create an OpenGL context for all available +OpenGL versions.

+ +

+The continously developed JOGL 2.x reflects the aforementioned OpenGL evolution +by mapping the OpenGL profiles to interfaces. +This is essential since creating an OpenGL context for each class of OpenGL profiles +requires it's specific initialisation.
+Some OpenGL profiles like + GLES2 +for embedded may not be available on desktop machines.

+ +

+Fixed Function (FFP) Only Profiles: +

GLES1

+ +

+Programmable Shader (PSP) Only Profiles: +

GLES2
GL3
GL4

+ +

+FFP & PSP Profiles: +

GL2
GL3bc
GL4bc

+ +

+The following UML diagram show that JOGL also adds common subsets of OpenGL profiles +to allow easy development of multiple target profiles.

+ +

+Common OpenGL Profile Subsets: +

+ +
+For example using the common interface +GL2ES2 +of GL2 +and GLES2, +ensures the code complies with the GL2 and GLES2 profile and an implementation may use both:

+    void renderSomethingForGL2(GL2 gl, int program) {
+        renderSomethingForGL2AndGLES2(gl, program);
+    }
+
+    void renderSomethingForGLES2(GLES2 gl, int program) {
+        renderSomethingForGL2AndGLES2(gl, program);
+    }
+
+    void renderSomethingForGL2AndGLES2(GL2ES2 gl, int program) {
+        gl.glValidateProgram(program);
+        ...
+
+    }
+

+ +