Example 1: Plain Texture

This is a working example of how to create a very simple shader. The shader just applies a single texture to an object. No lighting is performed.

First, create a .material file. The filename is unimportant, but make sure it's in a directory that the game is scanning for media. In the example applications, this is configured in 'resources.cfg'. Add the following material definition to the material file.

Make sure you have this line in the plugins.cfg file : Plugin=Plugin_CgProgramManager.

// CG Vertex shader definition
vertex_program PlainTexture_VS cg            
{
        // Look in this source file for shader code
    source GameObjStandard.cg
        // Use this function for the vertex shader            
    entry_point main_plain_texture_vp    
        // Compile the shader to vs_1_1 format    
    profiles vs_1_1                    

    // This block saves us from manually setting parameters in code
        default_params                    
    {
                // Ogre will put the worldviewproj into our 'worldViewProj' parameter for us.
        param_named_auto worldViewProj worldviewproj_matrix        
                // Note that 'worldViewProj' is a parameter in the cg code.
    }
}

// CG Pixel shader definition
fragment_program PlainTexture_PS cg            
{
        // Look in this source file for shader code
    source GameObjStandard.cg        
        // Use this function for the pixel shader    
    entry_point main_plain_texture_fp    
        // Compile to ps_1_1 format    
    profiles ps_1_1                    
}

material PlainTexture
{
        // Material has one technique
    technique                    
    {
                // This technique has one pass
        pass                    
        {
                        // Make this pass use the vertex shader defined above
            vertex_program_ref PlainTexture_VS    
            {
            }
                        // Make this pass use the pixel shader defined above
            fragment_program_ref PlainTexture_PS    
            {
            }
            texture_unit
            {
                                // This pass will use this 2D texture as its input
                texture Ten.png 2d        
            }
        }
    }
}


This material made references to another file which contains the CG pixel and vertex shaders. Create a file 'GameObjStandard.cg' (also in a media directory) and add the following block. This time the name of the file is important, as the material file refers specifically to it.

void main_plain_texture_vp(
        // Vertex Inputs
        float4 position        : POSITION,    // Vertex position in model space
        float2 texCoord0    : TEXCOORD0,    // Texture UV set 0

        // Outputs
        out float4 oPosition    : POSITION,    // Transformed vertex position
        out float2 uv0        : TEXCOORD0,    // UV0

        // Model Level Inputs
        uniform float4x4 worldViewProj)
{
    // Calculate output position
    oPosition = mul(worldViewProj, position);

    // Simply copy the input vertex UV to the output
    uv0 = texCoord0;
}

void main_plain_texture_fp(
        // Pixel Inputs
        float2 uv0        : TEXCOORD0,    // UV interpolated for current pixel
             
        // Outputs
        out float4 color    : COLOR,    // Output color we want to write
             
        // Model Level Inputs
        uniform sampler2D texture)        // Texture we're going to use
{
    // Just sample texture using supplied UV
    color = tex2D(texture, uv0);
}


The keyword uniform identifies the parameters you will have to supply in the material file.

  • Some parameters can be supplied by the Ogre Engine (param_named_auto), like a light position.
  • Some parameters can be supplied by your material file (param_named) like a texture map.
  • Some parameters can be supplied by your application (custom).




Finally, in the game code, you need to set the material on the entity. To do so, you'll want a line of code something like the following:

pOgreEntity->setMaterialName( "PlainTexture" );

The texture should render on the object. If the material failed to compile properly, it will render white.

Example 2: Texture with modulated color

Now let's say that we want to tweak our simple shader by modulating the texture with another color, and also specify an alpha value for the object.

Colors and modulation basics:

  • In shaders, color values are normally in the range 0..1. A pure red would be R=1, G=0, B=0.
  • A color can be stored in a float3, or a float4 with the fourth component containing alpha information.
  • The RGB components can be accessed as either .r, .g, .b, .a or .x, .y, .z, .w
  • Modulate means multiply. Let's take an example:
    • Lets say that reading the texture with the tex2D returns (R=1, G=0.5, B=0)
    • Lets say we then modulate that with a pink (R=1, G=0.25, B=0.25)
    • This gives an output of (1*1, 0.5*0.25, 0*0.25) = (1, 0.125, 0)
    • The result is that the source texture gets a pink tone to it. Note that modulating with numbers in the range 0..1 only makes things darker, and modulating low numbers together goes to black quickly.




First, define a new material. The key important notes are:

  • The vertex shader doesn't need to do anything different than before, so we're going to use the same one as the material before. We don't need to define a new 'vertex program', though a better naming than 'PlainTexture_VS' would have been more appropriate :-)
  • There's going to be a new pixel shader, so we define a new 'fragment program' block in the material file. It's the same as the last one except it has a different 'entry point' and it defines a default value for our new 'colorModulate' parameter.
  • The material 'pass' block now has a line 'scene_blend alpha_blend'. This means that the pixel shader alpha channel output will be used to blend the color with what's already in the frame buffer. An alpha output of 0 would cause the object to be invisible, and a value of 1 would make it entirely solid.
  • The 'fragment_program_ref' references the name of our new 'fragment program' block.



fragment_program TextureModColor_PS cg
{
    source GameObjStandard.cg
    
    // Different entry point for pixel shader
    entry_point main_tex_mod_col_fp
    
    profiles ps_1_1

    default_params
    {
        // Specify a default value for a new parameter
        // Note that we don't need to specify whether it's a pixel of vertex shader parameter
        param_named colorModulate float4 1 0 0 0.5        
    }
}

material TextureModColor
{
    technique
    {
        pass
        {
            // Makes the pixel shader alpha output be used for alpha blending
            scene_blend alpha_blend            
            
            vertex_program_ref PlainTexture_VS
            {
            }
            fragment_program_ref TextureModColor_PS
            {
            }
            texture_unit
            {
                texture Ten.png 2d
            }
        }
    }
}


Now add the following new pixel shader to your CG file. The key noteworthy changes from the first pixel shader are:

  • There's a new 'colorModulate' function. Note how the parameter name matches the default value set in the material.
  • After the texture sample, we modulate the texture with the new parameter.
  • The last line explicitly puts the alpha value from the parameter into the alpha channel of the output variable.
    • Actually this isn't strictly needed in my case. My texture doesn't have an alpha channel, so the texture sample just puts a 1 into the alpha channel. Then the modulate for the alpha channel operation makes gives color.a = 1 * colorModulate.a, which is the same as color.a = colorModulate.a. I'll leave the line in though as it demonstrates that you can assign values into RGBA too...



void main_tex_mod_col_fp(
            float2 diffuse        : TEXCOORD0,
             
            out float4 color    : COLOR,
             
            uniform float4 colorModulate,    // Added the color parameter
            uniform sampler2D texture)
{
    color = tex2D(texture, diffuse);        // Sample the texture
    color = color * colorModulate;            // Multiply the pixel color by colorModulate
    color.a = colorModulate.a;            // Set the output alpha to be colorModulate.w
}

Programmatic control of color parameter

So far the material we've defined applies a default color modulation and alpha value to the object. We can control this value dynamically from code on a per entity (or rather sub entity) basis. First we need to add a line to the 'fragment program ref' block in the material:

fragment_program_ref TextureModColor_PS
            {
                param_named_auto colorModulate custom 1
            }

This means that our parameter 'colorModulate' can be set from code by setting parameter '1'.

Now we add some lines to your test application at some point after the material is attached to the object. For example:

// Init material
    mEntity->setMaterialName( "TextureModColor" );

#define COLOR_MODULATE_PARAM_INDEX 1
    SubEntity* pSub = mEntity->getSubEntity(0);
    pSub->setCustomParameter(COLOR_MODULATE_PARAM_INDEX, Vector4(0.f, 0.f, 1.0f, 0.2f));

Further Reading/Learning


Alias: Getting_Started_With_Ogre_CG_Materials

<HR>
Creative Commons Copyright -- Some rights reserved.


THE WORK (AS DEFINED BELOW) IS PROVIDED UNDER THE TERMS OF THIS CREATIVE COMMONS PUBLIC LICENSE ("CCPL" OR "LICENSE"). THE WORK IS PROTECTED BY COPYRIGHT AND/OR OTHER APPLICABLE LAW. ANY USE OF THE WORK OTHER THAN AS AUTHORIZED UNDER THIS LICENSE OR COPYRIGHT LAW IS PROHIBITED.

BY EXERCISING ANY RIGHTS TO THE WORK PROVIDED HERE, YOU ACCEPT AND AGREE TO BE BOUND BY THE TERMS OF THIS LICENSE. THE LICENSOR GRANTS YOU THE RIGHTS CONTAINED HERE IN CONSIDERATION OF YOUR ACCEPTANCE OF SUCH TERMS AND CONDITIONS.

1. Definitions

  • "Collective Work" means a work, such as a periodical issue, anthology or encyclopedia, in which the Work in its entirety in unmodified form, along with a number of other contributions, constituting separate and independent works in themselves, are assembled into a collective whole. A work that constitutes a Collective Work will not be considered a Derivative Work (as defined below) for the purposes of this License.
  • "Derivative Work" means a work based upon the Work or upon the Work and other pre-existing works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which the Work may be recast, transformed, or adapted, except that a work that constitutes a Collective Work will not be considered a Derivative Work for the purpose of this License. For the avoidance of doubt, where the Work is a musical composition or sound recording, the synchronization of the Work in timed-relation with a moving image ("synching") will be considered a Derivative Work for the purpose of this License.
  • "Licensor" means the individual or entity that offers the Work under the terms of this License.
  • "Original Author" means the individual or entity who created the Work.
  • "Work" means the copyrightable work of authorship offered under the terms of this License.
  • "You" means an individual or entity exercising rights under this License who has not previously violated the terms of this License with respect to the Work, or who has received express permission from the Licensor to exercise rights under this License despite a previous violation.
  • "License Elements" means the following high-level license attributes as selected by Licensor and indicated in the title of this License: Attribution, ShareAlike.

2. Fair Use Rights

Nothing in this license is intended to reduce, limit, or restrict any rights arising from fair use, first sale or other limitations on the exclusive rights of the copyright owner under copyright law or other applicable laws.

3. License Grant

Subject to the terms and conditions of this License, Licensor hereby grants You a worldwide, royalty-free, non-exclusive, perpetual (for the duration of the applicable copyright) license to exercise the rights in the Work as stated below:

  • to reproduce the Work, to incorporate the Work into one or more Collective Works, and to reproduce the Work as incorporated in the Collective Works;
  • to create and reproduce Derivative Works;
  • to distribute copies or phonorecords of, display publicly, perform publicly, and perform publicly by means of a digital audio transmission the Work including as incorporated in Collective Works;
  • to distribute copies or phonorecords of, display publicly, perform publicly, and perform publicly by means of a digital audio transmission Derivative Works.
  • For the avoidance of doubt, where the work is a musical composition:
    • Performance Royalties Under Blanket Licenses. Licensor waives the exclusive right to collect, whether individually or via a performance rights society (e.g. ASCAP, BMI, SESAC), royalties for the public performance or public digital performance (e.g. webcast) of the Work.
    • Mechanical Rights and Statutory Royalties. Licensor waives the exclusive right to collect, whether individually or via a music rights society or designated agent (e.g. Harry Fox Agency), royalties for any phonorecord You create from the Work ("cover version") and distribute, subject to the compulsory license created by 17 USC Section 115 of the US Copyright Act (or the equivalent in other jurisdictions).
    • Webcasting Rights and Statutory Royalties. For the avoidance of doubt, where the Work is a sound recording, Licensor waives the exclusive right to collect, whether individually or via a performance-rights society (e.g. SoundExchange), royalties for the public digital performance (e.g. webcast) of the Work, subject to the compulsory license created by 17 USC Section 114 of the US Copyright Act (or the equivalent in other jurisdictions).


The above rights may be exercised in all media and formats whether now known or hereafter devised. The above rights include the right to make such modifications as are technically necessary to exercise the rights in other media and formats. All rights not expressly granted by Licensor are hereby reserved.

4. Restrictions

The license granted in Section 3 above is expressly made subject to and limited by the following restrictions:

  • You may distribute, publicly display, publicly perform, or publicly digitally perform the Work only under the terms of this License, and You must include a copy of, or the Uniform Resource Identifier for, this License with every copy or phonorecord of the Work You distribute, publicly display, publicly perform, or publicly digitally perform. You may not offer or impose any terms on the Work that alter or restrict the terms of this License or the recipients' exercise of the rights granted hereunder. You may not sublicense the Work. You must keep intact all notices that refer to this License and to the disclaimer of warranties. You may not distribute, publicly display, publicly perform, or publicly digitally perform the Work with any technological measures that control access or use of the Work in a manner inconsistent with the terms of this License Agreement. The above applies to the Work as incorporated in a Collective Work, but this does not require the Collective Work apart from the Work itself to be made subject to the terms of this License. If You create a Collective Work, upon notice from any Licensor You must, to the extent practicable, remove from the Collective Work any credit as required by clause 4(c), as requested. If You create a Derivative Work, upon notice from any Licensor You must, to the extent practicable, remove from the Derivative Work any credit as required by clause 4(c), as requested.
  • You may distribute, publicly display, publicly perform, or publicly digitally perform a Derivative Work only under the terms of this License, a later version of this License with the same License Elements as this License, or a Creative Commons iCommons license that contains the same License Elements as this License (e.g. Attribution-ShareAlike 2.5 Japan). You must include a copy of, or the Uniform Resource Identifier for, this License or other license specified in the previous sentence with every copy or phonorecord of each Derivative Work You distribute, publicly display, publicly perform, or publicly digitally perform. You may not offer or impose any terms on the Derivative Works that alter or restrict the terms of this License or the recipients' exercise of the rights granted hereunder, and You must keep intact all notices that refer to this License and to the disclaimer of warranties. You may not distribute, publicly display, publicly perform, or publicly digitally perform the Derivative Work with any technological measures that control access or use of the Work in a manner inconsistent with the terms of this License Agreement. The above applies to the Derivative Work as incorporated in a Collective Work, but this does not require the Collective Work apart from the Derivative Work itself to be made subject to the terms of this License.
  • If you distribute, publicly display, publicly perform, or publicly digitally perform the Work or any Derivative Works or Collective Works, You must keep intact all copyright notices for the Work and provide, reasonable to the medium or means You are utilizing: (i) the name of the Original Author (or pseudonym, if applicable) if supplied, and/or (ii) if the Original Author and/or Licensor designate another party or parties (e.g. a sponsor institute, publishing entity, journal) for attribution in Licensor's copyright notice, terms of service or by other reasonable means, the name of such party or parties; the title of the Work if supplied; to the extent reasonably practicable, the Uniform Resource Identifier, if any, that Licensor specifies to be associated with the Work, unless such URI does not refer to the copyright notice or licensing information for the Work; and in the case of a Derivative Work, a credit identifying the use of the Work in the Derivative Work (e.g., "French translation of the Work by Original Author," or "Screenplay based on original Work by Original Author"). Such credit may be implemented in any reasonable manner; provided, however, that in the case of a Derivative Work or Collective Work, at a minimum such credit will appear where any other comparable authorship credit appears and in a manner at least as prominent as such other comparable authorship credit.

5. Representations, Warranties and Disclaimer

UNLESS OTHERWISE AGREED TO BY THE PARTIES IN WRITING, LICENSOR OFFERS THE WORK AS-IS AND MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND CONCERNING THE MATERIALS, EXPRESS, IMPLIED, STATUTORY OR OTHERWISE, INCLUDING, WITHOUT LIMITATION, WARRANTIES OF TITLE, MERCHANTIBILITY, FITNESS FOR A PARTICULAR PURPOSE, NONINFRINGEMENT, OR THE ABSENCE OF LATENT OR OTHER DEFECTS, ACCURACY, OR THE PRESENCE OF ABSENCE OF ERRORS, WHETHER OR NOT DISCOVERABLE. SOME JURISDICTIONS DO NOT ALLOW THE EXCLUSION OF IMPLIED WARRANTIES, SO SUCH EXCLUSION MAY NOT APPLY TO YOU.

6. Limitation on Liability.

EXCEPT TO THE EXTENT REQUIRED BY APPLICABLE LAW, IN NO EVENT WILL LICENSOR BE LIABLE TO YOU ON ANY LEGAL THEORY FOR ANY SPECIAL, INCIDENTAL, CONSEQUENTIAL, PUNITIVE OR EXEMPLARY DAMAGES ARISING OUT OF THIS LICENSE OR THE USE OF THE WORK, EVEN IF LICENSOR HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

7. Termination

  • This License and the rights granted hereunder will terminate automatically upon any breach by You of the terms of this License. Individuals or entities who have received Derivative Works or Collective Works from You under this License, however, will not have their licenses terminated provided such individuals or entities remain in full compliance with those licenses. Sections 1, 2, 5, 6, 7, and 8 will survive any termination of this License.
  • Subject to the above terms and conditions, the license granted here is perpetual (for the duration of the applicable copyright in the Work). Notwithstanding the above, Licensor reserves the right to release the Work under different license terms or to stop distributing the Work at any time; provided, however that any such election will not serve to withdraw this License (or any other license that has been, or is required to be, granted under the terms of this License), and this License will continue in full force and effect unless terminated as stated above.

8. Miscellaneous

  • Each time You distribute or publicly digitally perform the Work or a Collective Work, the Licensor offers to the recipient a license to the Work on the same terms and conditions as the license granted to You under this License.
  • Each time You distribute or publicly digitally perform a Derivative Work, Licensor offers to the recipient a license to the original Work on the same terms and conditions as the license granted to You under this License.
  • If any provision of this License is invalid or unenforceable under applicable law, it shall not affect the validity or enforceability of the remainder of the terms of this License, and without further action by the parties to this agreement, such provision shall be reformed to the minimum extent necessary to make such provision valid and enforceable.
  • No term or provision of this License shall be deemed waived and no breach consented to unless such waiver or consent shall be in writing and signed by the party to be charged with such waiver or consent.
  • This License constitutes the entire agreement between the parties with respect to the Work licensed here. There are no understandings, agreements or representations with respect to the Work not specified here. Licensor shall not be bound by any additional provisions that may appear in any communication from You. This License may not be modified without the mutual written agreement of the Licensor and You.