It gives you the ability to constrain per-fragment ops to a rectangular portion of the screen, but without actually modifying the current viewport transform. So putting all of that together you can see why scissor test exists. Yes, scissor test can be faster can stencil because it's a simple accept/reject based on a fragment's screen space coords, whereas stencil needs to compare with the current value in the stencil buffer, possibly increment or decrement that current value, also take into account the results of the depth test, and so on. When a fragment is tested by the scissor test, it has therefore already been through the viewport transformation. The interface Since this code will be re-used throughout the tutorials, we will put the code in a separate file : common/controls.cpp, and declare the functions in common/controls.hpp so that tutorial06.cpp knows about them. Scissor test happens after the fragment shader, together with all of the other per-fragment operations that happen at that time, such as blending, depth/stencil, etc. Welcome for our 6th tutorial We will now learn how to use the mouse and the keyboard to move the camera just like in a FPS. it's relatively closely related to modelview and projection). If it helps to see where it conceptually fits in, think in terms of it being part of the transforms that are used to get your vertex data from world space to screen space (i.e. GlViewport actually specifies a transformation, and it's a transformation that happens after the vertex shader but before the fragment shader. They operate at two completely different parts of the graphics pipeline. Occasionally you come across an implementation that automatically scissors to the viewport region, but that violates the GL specification.īeyond that, the scissor rectangle can be used to temporarily restrict drawing to a sub-rectangle of the viewport, for special effects, UI elements, etc. So for example, the following code will clear the whole screen, even though the viewport is set to a small portion of the larger window: glViewport(200,200,100,100) Īdding glScissor() and enabling the scissor test (which is disabled by default) restricts the clear. glScissor() defines a screen space rectangle beyond which nothing is drawn (if the scissor test is enabled). So, you use glViewport() to determine the location and size of the screen space viewport region, but the rasterizer can still occasionally render pixels outside that region. Polygons are clipped to the edge of projection space, but other draw operations like glClear() are not. GlViewport() specifies a transformation from normalized projection space to screen space. You almost always want to set the scissor rectangle to the same values as the viewport. GlutTimerFunc(GAME_LOGIC_REFRESH_TIME, gameLogic, 0) Ĭalculations in move_ship are quite good close to center of the screen, but at the edges they are off enough, that it's a big problem and the player can't reach the edge of the screen.They are more complementary than alternatives to each other. GlutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH | GLUT_MULTISAMPLE) Void InitGLUTScene(const char* window_name) * helper functions for settings options and parameters */ In class we got the formula for doing this:ĭouble openglX = ((double)x - ) / * ĭouble openglY = -((double)y - ) / * Ĭonst float ar = (float)width / (float)height Everything works fine, the only problem is translating mouse coords (0,0 in top left corner) to openGL coords (0,0 in center of the screen). I need to make a game for a project on college.
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