OpenGL学习（4）——纹理（补）

完成章节后练习

练习

1. Make sure only the happy face looks in the other/reverse direction by changing the fragment shader.

#version 330 core
out vec4 FragColor;
in vec4 Color;
in vec2 texCoord;
uniform sampler2D texSampler1;
uniform sampler2D texSampler2;
void main()
{
    FragColor = mix(texture(texSampler1, texCoord)*Color, texture(texSampler2, vec2(-texCoord.x, texCoord.y)), 0.2);
}

2. Experiment with the different texture wrapping methods by specifying texture coordinates in the range 0.0f to 2.0f. See if you can display 4 smiley faces on a single container image clamped at its edge.

glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

3. Try to display only the center pixels of the texture image on the rectangle in such a way that the individual pixels are getting visible by changing the texture coordinates. Try to set the texture filtering method to GL_NEAREST to see the pixels more clearly.

float vertices[] = {0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 0.6f, 0.6f,
                    -0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 0.4f, 0.6f,
                    0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.6f, 0.4f,
                    -0.5f, -0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.4f, 0.4f};

glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_GL_LINEAR); //纹理被缩小时的过滤方式对该题没有影响
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

glBindTexture(GL_TEXTURE_2D, texture[1]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

4. Use a uniform variable as the mix function's third parameter to vary the amount the two textures are visible. Use the up and down arrow keys to change how much the container or the smiley face is visible.

#version 330 core
out vec4 FragColor;
in vec4 Color;
in vec2 texCoord;
uniform sampler2D texSampler1;
uniform sampler2D texSampler2;
uniform float ratio;
void main()
{
    FragColor = mix(texture(texSampler1, texCoord), texture(texSampler2, vec2(-texCoord.x, texCoord.y)), ratio);
}

ourShader.use();
flat fragmentRatio = 0.0f;
glUniform1f(glGetUniformLocation(ourShader.ID, "ratio"), fragmentRatio);
//render loop
while(!glfwWindowShouldClose(window)){
    processInput(window);
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    ourShader.use();
    if(glfwGetKey(window, GLFW_KEY_UP) == GLFW_PRESS){
        fragmentRatio += 0.01f;
        glUniform1f(glGetUniformLocation(ourShader.ID, "ratio"), fragmentRatio);
    }
    if(glfwGetKey(window, GLFW_KEY_DOWN) == GLFW_PRESS){
        fragmentRatio -= 0.01f;
        glUniform1f(glGetUniformLocation(ourShader.ID, "ratio"), fragmentRatio);
    }
    glBindVertexArray(VAO);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture[1]);
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
    glfwSwapBuffers(window);
    glfwPollEvents();
}