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POPositioning objects in a 3D Scene and then figuring out what the user clicked on
 

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    <p>I'm building a cross-platform game in C++, using OpenGL ES 2.0. The target is iPhone at the moment. I'm a newbie to coding games, but not a newbie to coding.</p> <p>I'm confused about how to architect the game. <strong>But specifically, I'm asking about how to setup the objects needed to position models in the scene.</strong></p> <p>I have an object that represents a scene. There are 5 scenes. Only one scene is shown at a time. A scene is like a game level. Each scene has all the code for rendering, game logic, mouse and keyboard handling. Touch-screen handling is handled like a mouse click.</p> <p>Each Scene has: It's own projection matrix. It's own "View" matrix -- currently not used -- always set to the identity matrix A list of models to render</p> <p>Each Model has: The vertex list A GLSL program to render itself A texture A "model" matrix</p> <p>I use an Orthographic projection matrix. </p> <p>Since we're using GLES 2, I have to do just about everything manually. Including the matrices. So I don't use glPushMatrix, glPopMatrix, glTranslate, etc. They aren't available. Instead, I have my own functions which operate on my own Matrix objects.</p> <p>OK here's where things get weird for me.</p> <p>1) Setup the projection matrix (using an orthographic matrix)</p> <pre><code>_math_matrix_ortho(&amp;this-&gt;ProjectionMatrix, 0.0, 1.0, 0.0, (float)height / (float)width, -1.0f, 1.0f); </code></pre> <p>2) Leave the view matrix as the identity matrix</p> <p>3) Load each model</p> <p>4) Each model's "model" matrix is defaults to the identity matrix</p> <p>5) I now scale each model to make them the right side in proportion to one another. The scaling function adjusts the Model's "model" matrix. </p> <pre><code>model-&gt;modelMatrix.Scale(0.25, 0.25, 0.25); </code></pre> <p>6) Move each model into place</p> <pre><code>model-&gt;modelMatrix.Translate(2.0, 0.0, 0.0); </code></pre> <p>7) Render each model</p> <pre><code>{ glUseProgram(this-&gt;_program.program); GL_CHECK_ERROR(); glVertexAttribPointer(_positionLoc, 3, GL_FLOAT, GL_FALSE, 0, _vertices ); GL_CHECK_ERROR(); glVertexAttribPointer(_texCoordLoc, 2, GL_FLOAT, GL_FALSE, 0, _texCoords); GL_CHECK_ERROR(); glEnableVertexAttribArray(_positionLoc); GL_CHECK_ERROR(); glEnableVertexAttribArray(_texCoordLoc); GL_CHECK_ERROR(); glBindTexture ( GL_TEXTURE_2D, _texture-&gt;getGLID() ); GL_CHECK_ERROR(); glUniform1i ( _texLoc, 0 ); GL_CHECK_ERROR(); glUniformMatrix4fv(_pMatrixLoc, 1, GL_FALSE, SceneManager::getInstance().getCurrentScene().ProjectionMatrix.m); GL_CHECK_ERROR(); glUniformMatrix4fv(_vMatrixLoc, 1, GL_FALSE, this-&gt;_vMatrix.m); GL_CHECK_ERROR(); glUniformMatrix4fv(_mMatrixLoc, 1, GL_FALSE, this-&gt;_mMatrix.m); GL_CHECK_ERROR(); glDrawArrays ( GL_TRIANGLE_STRIP, 0, 4); GL_CHECK_ERROR(); } </code></pre> <p>What seems odd to me right off: <strong>Is it appropriate to be translating the Model's matrix?</strong></p> <p>The dicey part comes when I try to glUnProject the mouse/touch-screen coordinates. </p> <p>1) Get Mouse/Touch-Screen coordinates</p> <p>2) Un-project them. </p> <p>Now I have the coordinates relative to the View matrix. Which is the identity matrix. What that means is that x,y coords are translated to a coordinate system where the max vertical and horizonal extents are exactly 1.0. </p> <p><strong>How do I figure out what object was clicked?</strong></p> <p>It seems that in order to answer my last question, I need to better understand where I positioned it. </p> <p>I think I've over-designed this. Help.</p>
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    1. COThanks Apple for Vertex Array objects and GLKit which has all math logic.
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