fixes #70: raster tile rendering as toggleable mode from vector

src/shader/raster_shader.cpp

@@ -0,0 +1,47 @@
+#include <llmr/shader/raster_shader.hpp>
+#include <llmr/shader/shaders.hpp>
+#include <llmr/platform/gl.hpp>
+
+#include <cstdio>
+
+using namespace llmr;
+
+RasterShader::RasterShader()
+    : Shader(
+         shaders[RASTER_SHADER].vertex,
+         shaders[RASTER_SHADER].fragment
+         ) {
+    if (!valid) {
+        fprintf(stderr, "invalid raster shader\n");
+        return;
+    }
+
+    a_pos = glGetAttribLocation(program, "a_pos");
+
+    u_matrix = glGetUniformLocation(program, "u_matrix");
+    u_opacity = glGetUniformLocation(program, "u_opacity");
+
+    // fprintf(stderr, "RasterShader:\n");
+    // fprintf(stderr, "    - u_matrix: %d\n", u_matrix);
+    // fprintf(stderr, "    - u_image: %d\n", u_image);
+    // fprintf(stderr, "    - u_opacity: %f\n", u_opacity);
+}
+
+void RasterShader::bind(char *offset) {
+    glEnableVertexAttribArray(a_pos);
+    glVertexAttribPointer(a_pos, 2, GL_SHORT, false, 0, offset);
+}
+
+void RasterShader::setImage(int32_t new_image) {
+    if (image != new_image) {
+        glUniform1i(u_image, new_image);
+        image = new_image;
+    }
+}
+
+void RasterShader::setOpacity(float new_opacity) {
+    if (opacity != new_opacity) {
+        glUniform1f(u_opacity, new_opacity);
+        opacity = new_opacity;
+    }
+}