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Assignment 4

Color Picking (20/25)

This will be the final project for this class.
Now that you have a checker/chess board, wouldn't it be fun to move any of the pieces? To do this you will need to "pick" a piece with the mouse. The easiest way I know is by making a color picker.

Extra: Use the pick to move any piece with the mouse.

Step 1: Create the shaders. The vertex shader is very simple.
void main() { gl_Position = projection * view * modelMatrix * vVertex; }
The fragment shader you need to write. Pass into the fragment shader an unsigned int containing the ID number for each piece. Convert that uint in to RGB-like values. Here's a hint:
float redColor = float(0x000000FF & colorID) / 255.0; float greenColor = float( (0x0000FF00 & colorID)>>8 ) / 255.0; float blueColor = float( (0x00FF0000 & colorID)>>16 ) / 255.0; float alphaColor = 0.0;

Step 2: Make a method to do the pick.
int Scene1::Pick(int x, int y) { glClearColor(1.0f, 1.0f, 1.0f, 0.0f); /// Paint the backgound white which is 0x00FFFFFF glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glBindBuffer(GL_UNIFORM_BUFFER, camera->GetMatriciesID()); Ref<ShaderComponent> shader = assetManager->GetComponent<ShaderComponent>("ColorPickingShader"); glUseProgram(shader->GetProgram()); for (GLuint i = 0; i < actors.size(); i++) { glUniformMatrix4fv(shader->GetUniformID("modelMatrix"), 1, GL_FALSE, actors[i]->GetModelMatrix()); glUniform1ui(shader->GetUniformID("colorID"), i); actors[i]->GetComponent<MeshComponent>()->Render(GL_TRIANGLES); } glUseProgram(0); GLuint colorIndex; glReadPixels(x, viewport.height-y, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, &colorIndex); colorIndex &= 0x00FFFFFF; /// This zeros out the alpha component if (colorIndex == 0x00FFFFFF) return -1; /// Picked nothing else return colorIndex; }
Step 3: Call Pick() from HandleEvents.