Ryan Joseph wrote: > Is it available in any version before 2.0 do you know? I don’t know > much about OpenGL but there is a 1.5 version also which maybe has > it. >
Before OpenGLES version 2.0 (shader pipeline), you only have OpenGLES 1.1 and OpenGLES 1.0. See https://en.wikipedia.org/wiki/OpenGL_ES and https://www.khronos.org/opengles/1_X/ . Although OpenGLES 1.1 was based on (desktop) OpenGL 1.5, which included glBlendEquation (you can see it in https://www.opengl.org/documentation/specs/version1.5/glspec15.pdf ). But I guess glBlendEquation was not included in OpenGLES for simplicity --- OpenGLES was, by design, a very "trimmed down" version of (desktop) OpenGL. And "glBlendEquation" is not available in OpenGLES 1.1. You have "glBlendFunc" in 1.1, but it only allows you to specify blending parameters, while blending equation is "hardcoded". Effectively, OpenGLES 1.1 always behaves like glBlendEquation(GL_FUNC_ADD) was called. You can see it e.g. by comparing glBlendFunc specifications for 1.1 and 2.0: - https://www.khronos.org/opengles/sdk/1.1/docs/man/glBlendFunc.xml , - https://www.khronos.org/opengles/sdk/docs/man/xhtml/glBlendFunc.xml In 1.1 version, the equation is simply hardcoded, while in 2.0 it can be configured by glBlendEquation. Hmm, but there's this extension: https://www.khronos.org/registry/gles/extensions/OES/OES_blend_subtract.txt . If this extension is supported, you could load glBlendEquationOES function, which should be what you need. I'm not sure why the thread on http://stackoverflow.com/questions/17457327/blending-issue-porting-from-opengles-1-0-to-2-0-ios suggests that glBlendEquation was used in OpenGLES 1.1. Maybe it's an Apple extension that, once you have OES_blend_subtract, you can load entry point "glBlendEquation", without "OES" suffix? Or maybe the poster on stackoverflow just simplified his/her code, to simplify the question? Regards, Michalis _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
