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POHow can I display multiple separate textures (not multi-texturing) with OpenGL ES 2.0?
 

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  1. POHow can I display multiple separate textures (not multi-texturing) with OpenGL ES 2.0?
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    <p>My iOS 4 app uses OpenGL ES 2.0 and renders elements with a single texture. I would like to draw elements using multiple different textures and am having problems getting things to work.</p> <p>I added a variable to my vertex shader to indicate which texture to apply:</p> <pre><code>... attribute float TextureIn; varying float TextureOut; void main(void) { ... TextureOut = TextureIn; } </code></pre> <p>I use that value in the fragment shader to select the texture:</p> <pre><code>... varying lowp float TextureOut; uniform sampler2D Texture0; uniform sampler2D Texture1; void main(void) { if (TextureOut == 1.0) { gl_FragColor = texture2D(Texture1, TexCoordOut); } else // 0 { gl_FragColor = texture2D(Texture0, TexCoordOut); } } </code></pre> <p>Compile shaders:</p> <pre><code>... _texture = glGetAttribLocation(programHandle, "TextureIn"); glEnableVertexAttribArray(_texture); _textureUniform0 = glGetUniformLocation(programHandle, "Texture0"); _textureUniform1 = glGetUniformLocation(programHandle, "Texture1"); </code></pre> <p>Init/Setup:</p> <pre><code>... GLuint _texture; GLuint _textureUniform0; GLuint _textureUniform1; ... glActiveTexture(GL_TEXTURE0); glEnable(GL_TEXTURE_2D); // ? glBindTexture(GL_TEXTURE_2D, _textureUniform0); glUniform1i(_textureUniform0, 0); glActiveTexture(GL_TEXTURE1); glEnable(GL_TEXTURE_2D); // ? glBindTexture(GL_TEXTURE_2D, _textureUniform1); glUniform1i(_textureUniform1, 1); glActiveTexture(GL_TEXTURE0); </code></pre> <p>Render:</p> <pre><code>... glVertexAttribPointer(_texture, 1, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*) (sizeof(float) * 13)); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, _textureUniform0); glUniform1i(_textureUniform0, 0); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, _textureUniform1); glUniform1i(_textureUniform1, 1); glActiveTexture(GL_TEXTURE0); glDrawElements(GL_TRIANGLES, indicesCountA, GL_UNSIGNED_SHORT, (GLvoid*) (sizeof(GLushort) * 0)); glDrawElements(GL_TRIANGLES, indicesCountB, GL_UNSIGNED_SHORT, (GLvoid*) (sizeof(GLushort) * indicesCountA)); glDrawElements(GL_TRIANGLES, indicesCountC, GL_UNSIGNED_SHORT, (GLvoid*) (sizeof(GLushort) * (indicesCountA + indicesCountB))); </code></pre> <p>My hope was to dynamically apply the texture associated with a vertex but it seems to only recognize GL_TEXTURE0.</p> <p>The only way I have been able to change textures is to associated each texture with GL_TEXTURE0 and then draw:</p> <pre><code>glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, _textureUniformX); glUniform1i(_textureUniformX, 0); glDrawElements(GL_TRIANGLES, indicesCountA, GL_UNSIGNED_SHORT, (GLvoid*) (sizeof(GLushort) * 0)); ... </code></pre> <p>In order to render all the textures, I would need a separate glDrawElements() call for each texture, and I have read that glDrawElements() calls are a big hit to performance and the number of calls should be minimized. Thats why I was trying to dynamically specifiy which texture to use for each vertex.</p> <p>It's entirely possible that my understanding is wrong or I am missing something important. I'm still new to OpenGL and the more I learn the more I feel I have more to learn.</p> <p>It must be possible to use textures other than just GL_TEXTURE0 but I have yet to figure out how.</p> <p>Any guidance or direction would be greatly appreciated.</p>
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