I decided to get off my backside and have a play about with GLSL today...started to enjoy playing about and making models wobble about using the vertex shader, and colours go funky with a fragment shader, but i'm having a hell of a lot of trouble trying to write a shader that will do texture splatting for me. If you have texturing enabled, BUT in a fragment shader you set gl_FragColor to any specific colour shouldn't the output be that colour? I decided to try this as no matter what my fragment shader said the output was the same, the vertex shader, however, affected what I was doing. Both shaders can be made to do things interesting until I introduce textures. I'll post some code and a screen shot to illustrate my problems, with the fragment shader I'm using shouldn't the output be ALL red? Also, the code i'm using to render has been hacked about, ill post it without sections i've commented out.
Vertex Shader
void main(void)
{
gl_TexCoord[0] = gl_MultiTexCoord0;
gl_TexCoord[1] = gl_MultiTexCoord1;
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}
Fragment Shader
void main (void)
{
vec4 texval1 = texture2D(0, vec2(gl_TexCoord[0]));
vec4 texval2 = texture2D(1, vec2(gl_TexCoord[1]));
gl_FragColor = vec4(1.0, 0.0, 0.0, 0.5); //0.5*(texval1+texval2);
}
Code which renders (removed commented out stuff)
void cTerrainRenderer::Render()
{
glUseProgramObjectARB(m_ShaderProgram);
// Setup the render state for 2D Texturing
// and Blending
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_COLOR_MATERIAL);
// Get the vertex, normal and texture arrays ready
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
// Pass in pointers for GL to use
glVertexPointer(3, GL_FLOAT, 0, m_pTerrainData->m_pVertexArray);
glNormalPointer(GL_FLOAT, 0, m_pTerrainData->m_pNormalArray);
// First loop through the layers
int l_iLayer = 3;
//for (int l_iLayer = 0; l_iLayer < m_pTerrainData->m_NumLayers; ++l_iLayer)
{
// Alpha Channel on Texture Unit 0
glActiveTextureARB(GL_TEXTURE0_ARB);
glClientActiveTextureARB(GL_TEXTURE0_ARB);
// Bind the texture
m_pRenderer->m_pTextureManager->BindTexture(m_pTerrainData->m_pTextureLayers[l_iLayer+1].m_DiffuseMap);
glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_EXT);
glTexEnvf (GL_TEXTURE_ENV, GL_COMBINE_RGB_EXT, GL_REPLACE);
// Give it some texture coordinates
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, m_pTerrainData->m_pTextureArray);
// Diffuse Map on Texture Unit 1
glActiveTextureARB(GL_TEXTURE1_ARB);
glClientActiveTextureARB(GL_TEXTURE1_ARB);
// Bind Texture
m_pRenderer->m_pTextureManager->BindTexture(m_pTerrainData->m_pTextureLayers[l_iLayer].m_DiffuseMap);
glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_EXT);
glTexEnvf (GL_TEXTURE_ENV, GL_COMBINE_RGB_EXT, GL_INCR);
// Give it some texture coordinates
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, m_pTerrainData->m_pTextureArray);
// Enter the Texture Matrix Mode :-D
glMatrixMode(GL_TEXTURE);
glPushMatrix();
// Translate the texture
glRotatef(m_pTerrainData->m_pTextureLayers[l_iLayer].m_Angle, 0.0f, 0.0f, 1.0f);
glScalef(m_pTerrainData->m_pTextureLayers[l_iLayer].m_Scale.X, m_pTerrainData->m_pTextureLayers[l_iLayer].m_Scale.Y, 0.0f);
// Loop through the fragment list
for (int l_iFragment = 0; l_iFragment < m_pTerrainData->m_NumFragments; ++l_iFragment)
{
// Send the polygons down the pipeline (experimental, no checks)
glDrawElements(GL_TRIANGLES, m_pTerrainData->m_pTerrainFragments[l_iFragment].m_NumIndices, GL_UNSIGNED_INT, m_pTerrainData->m_pTerrainFragments[l_iFragment].m_pIndices);
}
// Exit the Texture Matrix Mode :-O
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
// Now to unbind for the next run
// Diffuse Map on Texture Unit 1
glActiveTextureARB(GL_TEXTURE1_ARB);
glClientActiveTextureARB(GL_TEXTURE1_ARB);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
m_pRenderer->m_pTextureManager->UnBindTexture(m_pTerrainData->m_pTextureLayers[l_iLayer].m_DiffuseMap);
// Alpha Channel on Texture Unit 0
glActiveTextureARB(GL_TEXTURE0_ARB);
glClientActiveTextureARB(GL_TEXTURE0_ARB);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
m_pRenderer->m_pTextureManager->UnBindTexture(m_pTerrainData->m_pTextureLayers[l_iLayer+1].m_DiffuseMap);
}
// Restore the render state
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glDisable(GL_BLEND);
glUseProgramObjectARB(0);
}
And now what i actually get with that code:
I do a couple of translations on the rocky texture, and when I go up close there is actually a snowy texture...with my vertex shader these transformations shouldn't even take place should they? Up close on 'terrain':
Any help appreciated
