Game Engineering – Building Game Engine – Part 3

The main part of this assignment is to remove all the platform specific code that is present in the various graphics.xx.cpp files and create one platform independent graphics.cpp file. For this I created another class to hold all the platform specific code called “GraphicsHelper”. This class contained functions that mirror those of the main Graphics interface. Graphics.cpp contained all the platform independent code and calls are made to functions in graphics helper for platform dependent code. Each platform specific implementation inside GraphicsHelper is differentiated using preprocessor blocks.

The GraphicsHelper class also has interface to change the color of back buffer. At start of every frame the back buffer is first cleared usually by setting the color to black. I created a color struct that takes in values of red, green, blue and alpha between the values of 0 and 1. This I pass to my graphicshelper.cpp using the interface “SetBackBuffer” which then sets the value for the back buffer.


sColor m_BackBuffer {

abs(sin(s_dataBeingSubmittedByApplicationThread - > constantData_perFrame.g_elapsedSecondCount_simulationTime)), abs(cos(s_dataBeingSubmittedByApplicationThread - > constantData_perFrame.g_elapsedSecondCount_simulationTime)), abs(cos(s_dataBeingSubmittedByApplicationThread - > constantData_perFrame.g_elapsedSecondCount_simulationTime)), 1


Interface for changing the color of back buffer


We also added an index buffer to tell the graphics API, the order in which vertices of a triangle are to be drawn. By using an index buffer, we can reduce the number of points that are being stored for any shape as we can remove the common vertices between each triangle that is part of that mesh. But, this introduces an additional complexity when using different renderers such as OpenGL and DirectX. Since they render points in different order, index buffer for one is incompatible with the other. The way I solved this is to take the order of OpenGL as default and swap every 2nd and 3rd point in the array.

I also moved out the code to initialize the meshes and effects from their respective classes to Graphics.cpp. During the initialization from graphics.cpp the effect needs the locations of both the vertex and the fragment shaders as strings

	s_Effect->Initialize(m_vertShader1Location, m_fragShader1Location);
	s_Effect2->Initialize(m_vertShader2Location, m_fragShader2Location);

The mesh requires a pointer to the array containing the vertex buffer, pointer to an array containing index buffer and the number of vertices that are to be rendered using the index buffer, as it is not possible to find the number of vertices since we are passing a pointer to the array and not the array itself.

s_Mesh->Initialize(vertexData, indexData, 3);
s_Mesh2->Initialize(vertexData2, indexData2, 4);

After refactoring the code to include the changes to Graphics.cpp, my mesh class uses 28 Bytes and 48 bytes in OpenGL and Direct3D respectively. Effects on the other hand take-up 72 bytes and 120 bytes respectively. I could not find any way to reduce the size.

Optional Challenge:

As an optional challenge we must animate the background color. So instead of passing a solid color value such as {1,0,0,1} for red, I passed the value of the sine value of simulated time clamped between 0 and 1.

Final Output:

MyGame_x64 MyGame_x86</a

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