Mario certainly covered it! I recommend just getting the purple book
"OpenGL ES 2.0 Programming Guide" by Shreiner. It covers things
pretty well.
In short - ES 2.0 will not project it for you. You need to do that in
your vertex shader. It's pretty easy though. Something like:
uniform mat4 u_matViewProjection;
attribute vec4 a_position;
void main(void) {
gl_Position = u_matViewProjection * a_position;
}
Should do the trick.
On Apr 17, 4:31 am, Mario Zechner <[email protected]> wrote:
> Hi,
>
> OpenGL ES 2.0 (GLES2) is completely based on writting your own vertex
> and fragment shaders. Both types serve a specific purpose.
>
> Vertex shaders in their most basic form are responsible for
> transforming the incoming vertex position. This includes moving them
> from object to world space, from world space to camera or view space
> and finally projecting the camera/view space positions.
> Transformations and projections are achieved via matrices which you
> usually pass to your shader as so called uniforms. A vertex shader
> outputs the final vertex position and potentially other information
> for the fragment shader, like interpolated texture coordinates and
> normals. A vertex shader thus has to perform the equivalent of the
> fixed function pipeline transformation and lighting stage (with the
> later often being implemented in the fragment shader instead to get
> per pixel lighting).
>
> A fragment shader is responsible for outputting a fragments color
> based on various conditions. You might want to fetch a texel from a
> texture as the color, apply phong shading based on interpolated
> normals you receive from the vertex shader and so on.
>
> As you can see there's various types of parameters and arguments
> involved when programming shaders. In GLES2 there's 3 main types
> (there are other less frequently used types as well): attributes,
> uniforms and varyings. Attributes and uniforms are specified by you
> via calls to glVertexAttrib, glVertexAttribPointer or glUniform.
> Attributes represent vertex attributes like position, texture
> coordintates, per vertex colors or normals. Uniforms are normally used
> to pass in things like transformation and projection matrices that you
> calculate outside the shaders in your program. Varyings are generated
> within the vertex shader and passed to the fragment shader. Popular
> examples would be interpolated texture coordinates or normals for
> phong shading.
>
> So what does all this mean for your scenario? First, you will need to
> calculate the proper transformation and projection matrices yourself,
> keep track of them yourself and pass them in as uniforms to your
> vertex shader which then uses them to transform and project your
> vertices.
>
> There is no Android specific GLES2 reference as GLES2 is a standard
> developed by Khronos which keep the API the same for all platforms.
> The only difference between platforms is how to setup the GLES2
> context and buffers. Usually this is done via EGL, another standard by
> Khronos. On Android you can use the GLSurfaceView from the hello-gl2
> example for that purpose and not worry about it.
>
> To get information on the compilation process you can use the
> functions glGetShaderInfoLog (http://www.opengl.org/sdk/docs/man/xhtml/
> glGetShaderInfoLog.xml) and glGetProgramInfoLog (http://www.opengl.org/
> sdk/docs/man/xhtml/glGetProgramInfoLog.xml). You usually use the first
> one after you compiled a vertex or fragment shader and the second one
> after you linked together a vertex/fragment shader pair to a program.
> This will give you any errors or warnings the compiler produces. Note
> that the output is not standardized and will differ for different GPUs
> and their drivers.
>
> My advice would be to get the OpenGL ES 2.0 Programming Guide, a nice
> little book by the writers of the GLES2 standard which will guide you
> through all the features and standard procedures of GLES2. The basic
> concepts of GLES1 are still there in GLES2, however, you have a
> greater flexibility by providing your own implementation for various
> stages of the fixed function pipeline, including for example the
> transform and lighting stage.
>
> hth,
> Mario
>
> On 16 Apr., 06:20, HaMMeReD <[email protected]> wrote:
>
>
>
>
>
> > Working with NDK here.
>
> > How are perspective correct projection supposed to occur in es 2.0. I
> > can currently draw my geometry to the screen, but it is not getting
> > transformed to 2d.
>
> > Is there some sort of way of getting meaningful compiler errors out of
> > the shader compiler?
>
> > Is there a android specific reference to glsl support on it?
>
> > Am I even supposed to be doing projections in my glsl?
>
> > I was using "hello-gl2" as a baseline, and then modified it to load
> > additional geometry, which is rendering correctly although flat,
> > without any translation or projection. Any advice on translation/
> > projection is appreciated too, since it seems that all of that has
> > disappeared from es2.0.
>
> > I've got a opengl 1.1 live screensaver that I've developed that I want
> > to work on porting critical sections to NDK and es2.0, so any advice
> > on porting gl11 to gl20 is appreciated.
>
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