opengl 学习 之 10 lesson

opengl 学习 之 10 lesson

简介

透明度

简单来说让设定的透明度起作用。

link

http://www.opengl-tutorial.org/uncategorized/2017/06/07/website-update/

core code

	// Enable blending
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

==

New color in framebuffer =
 current alpha in framebuffer * current color in framebuffer +
 (1 - current alpha in framebuffer) * shader's output color

当前的在显存中的颜色 = 当前的透明度 * 颜色 + （1-当前透明度） * 经过着色器后输出的颜色

• 其实不是特别清楚上面这条公式，经过着色器输出的颜色是什么意思?
• 个人感觉Blend更倾向于颜色的相加

Example from the image above, with red on top :

new color = 0.5*(0,1,0) + (1-0.5)*(1,0.5,0.5); // (the red was already blended with the white background)
new color = (1, 0.75, 0.25) = the same orange

code

// Include standard headers
#include <stdio.h>
#include <stdlib.h>
#include <vector>

// Include GLEW
#include <GL/glew.h>

// Include GLFW
#include <GLFW/glfw3.h>
GLFWwindow* window;

// Include GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
using namespace glm;

#include <common/shader.hpp>
#include <common/texture.hpp>
#include <common/controls.hpp>
#include <common/objloader.hpp>
#include <common/vboindexer.hpp>

int main( void )
{
	// Initialise GLFW
	if( !glfwInit() )
	{
		fprintf( stderr, "Failed to initialize GLFW\n" );
		getchar();
		return -1;
	}

	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	// Open a window and create its OpenGL context
	window = glfwCreateWindow( 1024, 768, "Tutorial 10 - Transparency", NULL, NULL);
	if( window == NULL ){
		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
		getchar();
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	// Initialize GLEW
	glewExperimental = true; // Needed for core profile
	if (glewInit() != GLEW_OK) {
		fprintf(stderr, "Failed to initialize GLEW\n");
		getchar();
		glfwTerminate();
		return -1;
	}

	// Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
    // Hide the mouse and enable unlimited mouvement
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // Set the mouse at the center of the screen
    glfwPollEvents();
    glfwSetCursorPos(window, 1024/2, 768/2);

	// Dark blue background
	glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

	// Enable depth test
	glEnable(GL_DEPTH_TEST);
	// Accept fragment if it closer to the camera than the former one
	glDepthFunc(GL_LESS); 

	// Cull triangles which normal is not towards the camera
	//glEnable(GL_CULL_FACE); // Not this time !

	GLuint VertexArrayID;
	glGenVertexArrays(1, &VertexArrayID);
	glBindVertexArray(VertexArrayID);

	// Create and compile our GLSL program from the shaders
	GLuint programID = LoadShaders( "StandardShading.vertexshader", "StandardTransparentShading.fragmentshader" );

	// Get a handle for our "MVP" uniform
	GLuint MatrixID = glGetUniformLocation(programID, "MVP");
	GLuint ViewMatrixID = glGetUniformLocation(programID, "V");
	GLuint ModelMatrixID = glGetUniformLocation(programID, "M");

	// Load the texture
	GLuint Texture = loadDDS("uvmap.DDS");

	// Get a handle for our "myTextureSampler" uniform
	GLuint TextureID = glGetUniformLocation(programID, "myTextureSampler");

	// Read our .obj file
	std::vector<glm::vec3> vertices;
	std::vector<glm::vec2> uvs;
	std::vector<glm::vec3> normals;
	bool res = loadOBJ("suzanne.obj", vertices, uvs, normals);

	std::vector<unsigned short> indices;
	std::vector<glm::vec3> indexed_vertices;
	std::vector<glm::vec2> indexed_uvs;
	std::vector<glm::vec3> indexed_normals;
	indexVBO(vertices, uvs, normals, indices, indexed_vertices, indexed_uvs, indexed_normals);

	// Load it into a VBO

	GLuint vertexbuffer;
	glGenBuffers(1, &vertexbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
	glBufferData(GL_ARRAY_BUFFER, indexed_vertices.size() * sizeof(glm::vec3), &indexed_vertices[0], GL_STATIC_DRAW);

	GLuint uvbuffer;
	glGenBuffers(1, &uvbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
	glBufferData(GL_ARRAY_BUFFER, indexed_uvs.size() * sizeof(glm::vec2), &indexed_uvs[0], GL_STATIC_DRAW);

	GLuint normalbuffer;
	glGenBuffers(1, &normalbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, normalbuffer);
	glBufferData(GL_ARRAY_BUFFER, indexed_normals.size() * sizeof(glm::vec3), &indexed_normals[0], GL_STATIC_DRAW);

	// Generate a buffer for the indices as well
	GLuint elementbuffer;
	glGenBuffers(1, &elementbuffer);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned short), &indices[0], GL_STATIC_DRAW);

	// Get a handle for our "LightPosition" uniform
	glUseProgram(programID);
	GLuint LightID = glGetUniformLocation(programID, "LightPosition_worldspace");

	// For speed computation
	double lastTime = glfwGetTime();
	int nbFrames = 0;

	// Enable blending
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	do{

		// Measure speed
		double currentTime = glfwGetTime();
		nbFrames++;
		if ( currentTime - lastTime >= 1.0 ){ // If last prinf() was more than 1sec ago
			// printf and reset
			printf("%f ms/frame\n", 1000.0/double(nbFrames));
			nbFrames = 0;
			lastTime += 1.0;
		}

		// Clear the screen
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// Use our shader
		glUseProgram(programID);

		// Compute the MVP matrix from keyboard and mouse input
		computeMatricesFromInputs();
		glm::mat4 ProjectionMatrix = getProjectionMatrix();
		glm::mat4 ViewMatrix = getViewMatrix();
		glm::mat4 ModelMatrix = glm::mat4(1.0);
		glm::mat4 MVP = ProjectionMatrix * ViewMatrix * ModelMatrix;

		// Send our transformation to the currently bound shader,
		// in the "MVP" uniform
		glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);
		glUniformMatrix4fv(ModelMatrixID, 1, GL_FALSE, &ModelMatrix[0][0]);
		glUniformMatrix4fv(ViewMatrixID, 1, GL_FALSE, &ViewMatrix[0][0]);

		glm::vec3 lightPos = glm::vec3(4,4,4);
		glUniform3f(LightID, lightPos.x, lightPos.y, lightPos.z);

		// Bind our texture in Texture Unit 0
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, Texture);
		// Set our "myTextureSampler" sampler to use Texture Unit 0
		glUniform1i(TextureID, 0);

		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);

		// 2nd attribute buffer : UVs
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
		glVertexAttribPointer(
			1,                                // attribute
			2,                                // size
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);

		// 3rd attribute buffer : normals
		glEnableVertexAttribArray(2);
		glBindBuffer(GL_ARRAY_BUFFER, normalbuffer);
		glVertexAttribPointer(
			2,                                // attribute
			3,                                // size
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);

		// Index buffer
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer);

		// Draw the triangles !
		glDrawElements(
			GL_TRIANGLES,      // mode
			indices.size(),    // count
			GL_UNSIGNED_SHORT, // type
			(void*)0           // element array buffer offset
		);

		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);
		glDisableVertexAttribArray(2);

		// Swap buffers
		glfwSwapBuffers(window);
		glfwPollEvents();

	} // Check if the ESC key was pressed or the window was closed
	while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
		   glfwWindowShouldClose(window) == 0 );

	// Cleanup VBO and shader
	glDeleteBuffers(1, &vertexbuffer);
	glDeleteBuffers(1, &uvbuffer);
	glDeleteBuffers(1, &normalbuffer);
	glDeleteBuffers(1, &elementbuffer);
	glDeleteProgram(programID);
	glDeleteTextures(1, &Texture);
	glDeleteVertexArrays(1, &VertexArrayID);

	// Close OpenGL window and terminate GLFW
	glfwTerminate();

	return 0;
}

#version 330 core

// Interpolated values from the vertex shaders
in vec2 UV;
in vec3 Position_worldspace;
in vec3 Normal_cameraspace;
in vec3 EyeDirection_cameraspace;
in vec3 LightDirection_cameraspace;

// Ouput data
out vec4 color;

// Values that stay constant for the whole mesh.
uniform sampler2D myTextureSampler;
uniform mat4 MV;
uniform vec3 LightPosition_worldspace;

void main(){

	// Light emission properties
	// You probably want to put them as uniforms
	vec3 LightColor = vec3(1,1,1);
	float LightPower = 50.0f;

	// Material properties
	vec3 MaterialDiffuseColor = texture( myTextureSampler, UV ).rgb;
	vec3 MaterialAmbientColor = vec3(0.1,0.1,0.1) * MaterialDiffuseColor;
	vec3 MaterialSpecularColor = vec3(0.3,0.3,0.3);

	// Distance to the light
	float distance = length( LightPosition_worldspace - Position_worldspace );

	// Normal of the computed fragment, in camera space
	vec3 n = normalize( Normal_cameraspace );
	// Direction of the light (from the fragment to the light)
	vec3 l = normalize( LightDirection_cameraspace );
	// Cosine of the angle between the normal and the light direction,
	// clamped above 0
	//  - light is at the vertical of the triangle -> 1
	//  - light is perpendicular to the triangle -> 0
	//  - light is behind the triangle -> 0
	float cosTheta = clamp( dot( n,l ), 0,1 );

	// Eye vector (towards the camera)
	vec3 E = normalize(EyeDirection_cameraspace);
	// Direction in which the triangle reflects the light
	vec3 R = reflect(-l,n);
	// Cosine of the angle between the Eye vector and the Reflect vector,
	// clamped to 0
	//  - Looking into the reflection -> 1
	//  - Looking elsewhere -> < 1
	float cosAlpha = clamp( dot( E,R ), 0,1 );

	color.rgb =
		// Ambient : simulates indirect lighting
		MaterialAmbientColor +
		// Diffuse : "color" of the object
		MaterialDiffuseColor * LightColor * LightPower * cosTheta / (distance*distance) +
		// Specular : reflective highlight, like a mirror
		MaterialSpecularColor * LightColor * LightPower * pow(cosAlpha,5) / (distance*distance);

	color.a = 0.3;
}

#version 330 core

// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec3 vertexPosition_modelspace;
layout(location = 1) in vec2 vertexUV;
layout(location = 2) in vec3 vertexNormal_modelspace;

// Output data ; will be interpolated for each fragment.
out vec2 UV;
out vec3 Position_worldspace;
out vec3 Normal_cameraspace;
out vec3 EyeDirection_cameraspace;
out vec3 LightDirection_cameraspace;

// Values that stay constant for the whole mesh.
uniform mat4 MVP;
uniform mat4 V;
uniform mat4 M;
uniform vec3 LightPosition_worldspace;

void main(){

	// Output position of the vertex, in clip space : MVP * position
	gl_Position =  MVP * vec4(vertexPosition_modelspace,1);

	// Position of the vertex, in worldspace : M * position
	Position_worldspace = (M * vec4(vertexPosition_modelspace,1)).xyz;

	// Vector that goes from the vertex to the camera, in camera space.
	// In camera space, the camera is at the origin (0,0,0).
	vec3 vertexPosition_cameraspace = ( V * M * vec4(vertexPosition_modelspace,1)).xyz;
	EyeDirection_cameraspace = vec3(0,0,0) - vertexPosition_cameraspace;

	// Vector that goes from the vertex to the light, in camera space. M is ommited because it's identity.
	vec3 LightPosition_cameraspace = ( V * vec4(LightPosition_worldspace,1)).xyz;
	LightDirection_cameraspace = LightPosition_cameraspace + EyeDirection_cameraspace;

	// Normal of the the vertex, in camera space
	Normal_cameraspace = ( V * M * vec4(vertexNormal_modelspace,0)).xyz; // Only correct if ModelMatrix does not scale the model ! Use its inverse transpose if not.

	// UV of the vertex. No special space for this one.
	UV = vertexUV;
}